From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E94F0C433F5 for ; Mon, 10 Sep 2018 02:33:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DF632086E for ; Mon, 10 Sep 2018 02:33:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7DF632086E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726426AbeIJHYq (ORCPT ); Mon, 10 Sep 2018 03:24:46 -0400 Received: from mga17.intel.com ([192.55.52.151]:51315 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725906AbeIJHYq (ORCPT ); Mon, 10 Sep 2018 03:24:46 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Sep 2018 19:04:30 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,354,1531810800"; d="scan'208";a="255830880" Received: from btwcube1.sh.intel.com (HELO debian) ([10.67.104.194]) by orsmga005.jf.intel.com with ESMTP; 09 Sep 2018 19:04:26 -0700 Date: Mon, 10 Sep 2018 10:03:29 +0800 From: Tiwei Bie To: "Michael S. Tsirkin" Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, virtio-dev@lists.oasis-open.org, wexu@redhat.com, jfreimann@redhat.com Subject: Re: [PATCH net-next v2 3/5] virtio_ring: add packed ring support Message-ID: <20180910020329.GA9076@debian> References: <20180711022711.7090-1-tiwei.bie@intel.com> <20180711022711.7090-4-tiwei.bie@intel.com> <20180907083500-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180907083500-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 07, 2018 at 09:49:14AM -0400, Michael S. Tsirkin wrote: > On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie wrote: > > This commit introduces the support (without EVENT_IDX) for > > packed ring. > > > > Signed-off-by: Tiwei Bie > > --- > > drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++- > > 1 file changed, 487 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index c4f8abc7445a..f317b485ba54 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -55,12 +55,21 @@ > > #define END_USE(vq) > > #endif > > > > +#define _VRING_DESC_F_AVAIL(b) ((__u16)(b) << 7) > > +#define _VRING_DESC_F_USED(b) ((__u16)(b) << 15) > > Underscore followed by an upper case letter isn't a good idea > for a symbol. And it's not nice that this does not > use the VRING_DESC_F_USED from the header. > How about ((b) ? VRING_DESC_F_USED : 0) instead? > Is produced code worse then? Yes, I think the produced code is worse when we use conditional expression. Below is a simple test: #define foo1(b) ((b) << 10) #define foo2(b) ((b) ? (1 << 10) : 0) unsigned short bar(unsigned short b) { return foo1(b); } unsigned short baz(unsigned short b) { return foo2(b); } With `gcc -O3 -S`, I got below assembly code: .file "tmp.c" .text .p2align 4,,15 .globl bar .type bar, @function bar: .LFB0: .cfi_startproc movl %edi, %eax sall $10, %eax ret .cfi_endproc .LFE0: .size bar, .-bar .p2align 4,,15 .globl baz .type baz, @function baz: .LFB1: .cfi_startproc xorl %eax, %eax testw %di, %di setne %al sall $10, %eax ret .cfi_endproc .LFE1: .size baz, .-baz .ident "GCC: (Debian 8.2.0-4) 8.2.0" .section .note.GNU-stack,"",@progbits That is to say, for `((b) << 10)`, it will shift the register directly. But for `((b) ? (1 << 10) : 0)`, in above code, it will zero eax first, and set al to 1 depend on whether di is 0, and shift eax. > > > + > > struct vring_desc_state { > > void *data; /* Data for callback. */ > > struct vring_desc *indir_desc; /* Indirect descriptor, if any. */ > > }; > > > > struct vring_desc_state_packed { > > + void *data; /* Data for callback. */ > > + struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */ > > Include vring_desc_state for these? Sure. > > > + int num; /* Descriptor list length. */ > > + dma_addr_t addr; /* Buffer DMA addr. */ > > + u32 len; /* Buffer length. */ > > + u16 flags; /* Descriptor flags. */ > > This seems only to be used for indirect. Check indirect field above > instead and drop this. The `flags` is also needed to know the direction, i.e. DMA_FROM_DEVICE or DMA_TO_DEVICE when do DMA unmap. > > > int next; /* The next desc state. */ > > Packing things into 16 bit integers will help reduce > cache pressure here. > > Also, this is only used for unmap, so when dma API is not used, > maintaining addr and len list management is unnecessary. How about we > maintain addr/len in a separate array, avoiding accesses on unmap in that case? Sure. I'll give it a try. > > Also, lots of architectures have a nop unmap in the DMA API. > See a proposed patch at the end for optimizing that case. Got it. Thanks. > > > }; > > > > @@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > - virtio_mb(vq->weak_barriers); > > return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx); > > } > > why is this changing the split queue implementation? Because above barrier is also needed by virtqueue_poll_packed(), so I moved it to virtqueue_poll() and also added some comments for it. > > > > > > @@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int num, unsigned long align) > > & ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2; > > } > > > > +static void vring_unmap_state_packed(const struct vring_virtqueue *vq, > > + struct vring_desc_state_packed *state) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = state->flags; > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static void vring_unmap_desc_packed(const struct vring_virtqueue *vq, > > + struct vring_packed_desc *desc) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, desc->flags); > > I see no reason to use virtioXX wrappers for the packed ring. > That's there to support legacy devices. Just use leXX. Okay. > > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue *_vq, > > + unsigned int total_sg, > > + gfp_t gfp) > > +{ > > + struct vring_packed_desc *desc; > > + > > + /* > > + * We require lowmem mappings for the descriptors because > > + * otherwise virt_to_phys will give us bogus addresses in the > > + * virtqueue. > > Where is virt_to_phys used? I don't see it in this patch. In vring_map_single(), virt_to_phys() will be used to translate the address to phys if dma api isn't used: https://github.com/torvalds/linux/blob/a49a9dcce802/drivers/virtio/virtio_ring.c#L197 > > > + */ > > + gfp &= ~__GFP_HIGHMEM; > > + > > + desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp); > > + > > + return desc; > > +} > > + > > static inline int virtqueue_add_packed(struct virtqueue *_vq, > > struct scatterlist *sgs[], > > unsigned int total_sg, > > @@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > void *ctx, > > gfp_t gfp) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + struct vring_packed_desc *desc; > > + struct scatterlist *sg; > > + unsigned int i, n, descs_used, uninitialized_var(prev), err_idx; > > + __virtio16 uninitialized_var(head_flags), flags; > > + u16 head, avail_wrap_counter, id, curr; > > + bool indirect; > > + > > + START_USE(vq); > > + > > + BUG_ON(data == NULL); > > + BUG_ON(ctx && vq->indirect); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return -EIO; > > + } > > + > > +#ifdef DEBUG > > + { > > + ktime_t now = ktime_get(); > > + > > + /* No kick or get, with .1 second between? Warn. */ > > + if (vq->last_add_time_valid) > > + WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time)) > > + > 100); > > + vq->last_add_time = now; > > + vq->last_add_time_valid = true; > > + } > > +#endif > > Add incline helpers for this debug stuff rather than > duplicate it from split ring? Sure. I'd like to do that. > > > > + > > + BUG_ON(total_sg == 0); > > + > > + head = vq->next_avail_idx; > > + avail_wrap_counter = vq->avail_wrap_counter; > > + > > + if (virtqueue_use_indirect(_vq, total_sg)) > > + desc = alloc_indirect_packed(_vq, total_sg, gfp); > > + else { > > + desc = NULL; > > + WARN_ON_ONCE(total_sg > vq->vring_packed.num && !vq->indirect); > > + } > > > Apparently this attempts to treat indirect descriptors same as > direct ones. This is how it is in the split ring, but not in > the packed one. I think you want two separate functions, for > direct and indirect. Okay, I'll do that. > > > + > > + if (desc) { > > + /* Use a single buffer which doesn't continue */ > > + indirect = true; > > + /* Set up rest to use this indirect table. */ > > + i = 0; > > + descs_used = 1; > > + } else { > > + indirect = false; > > + desc = vq->vring_packed.desc; > > + i = head; > > + descs_used = total_sg; > > + } > > + > > + if (vq->vq.num_free < descs_used) { > > + pr_debug("Can't add buf len %i - avail = %i\n", > > + descs_used, vq->vq.num_free); > > + /* FIXME: for historical reasons, we force a notify here if > > + * there are outgoing parts to the buffer. Presumably the > > + * host should service the ring ASAP. */ > > + if (out_sgs) > > + vq->notify(&vq->vq); > > + if (indirect) > > + kfree(desc); > > + END_USE(vq); > > + return -ENOSPC; > > + } > > + > > + id = vq->free_head; > > + BUG_ON(id == vq->vring_packed.num); > > + > > + curr = id; > > + for (n = 0; n < out_sgs + in_sgs; n++) { > > + for (sg = sgs[n]; sg; sg = sg_next(sg)) { > > + dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ? > > + DMA_TO_DEVICE : DMA_FROM_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | > > + (n < out_sgs ? 0 : VRING_DESC_F_WRITE) | > > + _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) | > > + _VRING_DESC_F_USED(!vq->avail_wrap_counter)); > > Spec says: > The VIRTQ_DESC_F_WRITE flags bit is the only valid flag for descriptors in the > indirect table. > > All this logic isn't needed for indirect. > > Also, why re-calculate avail/used flags every time? They only change > when you wrap around. Will do that. Thanks. > > > > + if (!indirect && i == head) > > + head_flags = flags; > > + else > > + desc[i].flags = flags; > > + > > + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); > > + desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length); > > + i++; > > + if (!indirect) { > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[curr].addr = addr; > > + vq->desc_state_packed[curr].len = > > + sg->length; > > + vq->desc_state_packed[curr].flags = > > + virtio16_to_cpu(_vq->vdev, > > + flags); > > + } > > + curr = vq->desc_state_packed[curr].next; > > + > > + if (i >= vq->vring_packed.num) { > > + i = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + } > > + } > > + } > > + > > + prev = (i > 0 ? i : vq->vring_packed.num) - 1; > > + desc[prev].id = cpu_to_virtio16(_vq->vdev, id); > > Is it easier to write this out in all descriptors, to avoid the need to > calculate prev? Yeah, I'll do that. > > > + > > + /* Last one doesn't continue. */ > > + if (total_sg == 1) > > + head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > > + else > > + desc[prev].flags &= cpu_to_virtio16(_vq->vdev, > > + ~VRING_DESC_F_NEXT); > > Wouldn't it be easier to avoid setting VRING_DESC_F_NEXT > in the first place? > if (n != in_sgs - 1 && n != out_sgs - 1) Will this affect the branch prediction? > > must be better than writing descriptor an extra time. Not quite sure about this. I think this descriptor has just been written, it should still be in the cache. > > > + > > + if (indirect) { > > + /* Now that the indirect table is filled in, map it. */ > > + dma_addr_t addr = vring_map_single( > > + vq, desc, total_sg * sizeof(struct vring_packed_desc), > > + DMA_TO_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT | > > + _VRING_DESC_F_AVAIL(avail_wrap_counter) | > > + _VRING_DESC_F_USED(!avail_wrap_counter)); > > + vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev, > > + addr); > > + vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev, > > + total_sg * sizeof(struct vring_packed_desc)); > > + vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id); > > + > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[id].addr = addr; > > + vq->desc_state_packed[id].len = total_sg * > > + sizeof(struct vring_packed_desc); > > + vq->desc_state_packed[id].flags = > > + virtio16_to_cpu(_vq->vdev, head_flags); > > + } > > + } > > + > > + /* We're using some buffers from the free list. */ > > + vq->vq.num_free -= descs_used; > > + > > + /* Update free pointer */ > > + if (indirect) { > > + n = head + 1; > > + if (n >= vq->vring_packed.num) { > > + n = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + vq->next_avail_idx = n; > > + vq->free_head = vq->desc_state_packed[id].next; > > + } else { > > + vq->next_avail_idx = i; > > + vq->free_head = curr; > > + } > > + > > + /* Store token and indirect buffer state. */ > > + vq->desc_state_packed[id].num = descs_used; > > + vq->desc_state_packed[id].data = data; > > + if (indirect) > > + vq->desc_state_packed[id].indir_desc = desc; > > + else > > + vq->desc_state_packed[id].indir_desc = ctx; > > + > > + /* A driver MUST NOT make the first descriptor in the list > > + * available before all subsequent descriptors comprising > > + * the list are made available. */ > > + virtio_wmb(vq->weak_barriers); > > + vq->vring_packed.desc[head].flags = head_flags; > > + vq->num_added += descs_used; > > + > > + pr_debug("Added buffer head %i to %p\n", head, vq); > > + END_USE(vq); > > + > > + return 0; > > + > > +unmap_release: > > + err_idx = i; > > + i = head; > > + > > + for (n = 0; n < total_sg; n++) { > > + if (i == err_idx) > > + break; > > + vring_unmap_desc_packed(vq, &desc[i]); > > + i++; > > + if (!indirect && i >= vq->vring_packed.num) > > + i = 0; > > + } > > + > > + vq->avail_wrap_counter = avail_wrap_counter; > > + > > + if (indirect) > > + kfree(desc); > > + > > + END_USE(vq); > > return -EIO; > > } > > > > static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 flags; > > + bool needs_kick; > > + u32 snapshot; > > + > > + START_USE(vq); > > + /* We need to expose the new flags value before checking notification > > + * suppressions. */ > > + virtio_mb(vq->weak_barriers); > > + > > + snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); > > + flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; > > What are all these hard-coded things? Also either we do READ_ONCE > everywhere or nowhere. Why is this place special? Any why read 32 bit > if you only want the 16? Yeah, READ_ONCE() and reading 32bits are not really needed in this patch. But it's needed in the next patch. I thought it's not wrong to do this, so I introduced them from the first place. Just to double check: is the below code (apart from the hard-coded value and virtio16) from the next patch OK? """ snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); + off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff)); flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; """ > > And doesn't sparse complain about cast to __virtio16? I'll give it a try in the next version. > > > + > > +#ifdef DEBUG > > + if (vq->last_add_time_valid) { > > + WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), > > + vq->last_add_time)) > 100); > > + } > > + vq->last_add_time_valid = false; > > +#endif > > + > > + needs_kick = (flags != VRING_EVENT_F_DISABLE); > > + END_USE(vq); > > + return needs_kick; > > +} > > + > > +static void detach_buf_packed(struct vring_virtqueue *vq, > > + unsigned int id, void **ctx) > > +{ > > + struct vring_desc_state_packed *state = NULL; > > + struct vring_packed_desc *desc; > > + unsigned int curr, i; > > + > > + /* Clear data ptr. */ > > + vq->desc_state_packed[id].data = NULL; > > + > > + curr = id; > > + for (i = 0; i < vq->desc_state_packed[id].num; i++) { > > + state = &vq->desc_state_packed[curr]; > > + vring_unmap_state_packed(vq, state); > > + curr = state->next; > > + } > > + > > + BUG_ON(state == NULL); > > + vq->vq.num_free += vq->desc_state_packed[id].num; > > + state->next = vq->free_head; > > + vq->free_head = id; > > + > > + if (vq->indirect) { > > + u32 len; > > + > > + /* Free the indirect table, if any, now that it's unmapped. */ > > + desc = vq->desc_state_packed[id].indir_desc; > > + if (!desc) > > + return; > > + > > + if (vring_use_dma_api(vq->vq.vdev)) { > > + len = vq->desc_state_packed[id].len; > > + for (i = 0; i < len / sizeof(struct vring_packed_desc); > > + i++) > > + vring_unmap_desc_packed(vq, &desc[i]); > > + } > > + kfree(desc); > > + vq->desc_state_packed[id].indir_desc = NULL; > > + } else if (ctx) { > > + *ctx = vq->desc_state_packed[id].indir_desc; > > + } > > +} > > + > > +static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > > + u16 idx, bool used_wrap_counter) > > +{ > > + u16 flags; > > + bool avail, used; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, > > + vq->vring_packed.desc[idx].flags); > > + avail = !!(flags & VRING_DESC_F_AVAIL); > > + used = !!(flags & VRING_DESC_F_USED); > > + > > + return avail == used && used == used_wrap_counter; > > I think that you don't need to look at avail flag to detect a used > descriptor. The reason device writes it is to avoid confusing > *device* next time descriptor wraps. Okay, I'll just check the used flag. > > > } > > > > static inline bool more_used_packed(const struct vring_virtqueue *vq) > > { > > - return false; > > + return is_used_desc_packed(vq, vq->last_used_idx, > > + vq->used_wrap_counter); > > } > > > > static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > unsigned int *len, > > void **ctx) > > { > > - return NULL; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 last_used, id; > > + void *ret; > > + > > + START_USE(vq); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return NULL; > > + } > > + > > + if (!more_used_packed(vq)) { > > + pr_debug("No more buffers in queue\n"); > > + END_USE(vq); > > + return NULL; > > + } > > + > > + /* Only get used elements after they have been exposed by host. */ > > + virtio_rmb(vq->weak_barriers); > > + > > + last_used = vq->last_used_idx; > > + id = virtio16_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].id); > > + *len = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].len); > > + > > + if (unlikely(id >= vq->vring_packed.num)) { > > + BAD_RING(vq, "id %u out of range\n", id); > > + return NULL; > > + } > > + if (unlikely(!vq->desc_state_packed[id].data)) { > > + BAD_RING(vq, "id %u is not a head!\n", id); > > + return NULL; > > + } > > + > > + vq->last_used_idx += vq->desc_state_packed[id].num; > > + if (vq->last_used_idx >= vq->vring_packed.num) { > > + vq->last_used_idx -= vq->vring_packed.num; > > + vq->used_wrap_counter ^= 1; > > + } > > + > > + /* detach_buf_packed clears data, so grab it now. */ > > + ret = vq->desc_state_packed[id].data; > > + detach_buf_packed(vq, id, ctx); > > + > > +#ifdef DEBUG > > + vq->last_add_time_valid = false; > > +#endif > > + > > + END_USE(vq); > > + return ret; > > } > > > > static void virtqueue_disable_cb_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_DISABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > } > > > > static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > { > > - return 0; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > + > > + END_USE(vq); > > + return vq->last_used_idx | ((u16)vq->used_wrap_counter << 15); > > } > > > > -static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned last_used_idx) > > +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned off_wrap) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + bool wrap_counter; > > + u16 used_idx; > > + > > + wrap_counter = off_wrap >> 15; > > + used_idx = off_wrap & ~(1 << 15); > > + > > + return is_used_desc_packed(vq, used_idx, wrap_counter); > > These >> 15 << 15 all over the place duplicate info. > Pls put 15 in the header. Sure. > > Also can you maintain the counters properly shifted? > Then just use them. Then, we may need to maintain both of the shifted wrapper counters and un-shifted wrapper counters at the same time. > > > > } > > > > static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > + } > > + > > + if (more_used_packed(vq)) { > > + END_USE(vq); > > + return false; > > + } > > + > > + END_USE(vq); > > + return true; > > } > > > > static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + unsigned int i; > > + void *buf; > > + > > + START_USE(vq); > > + > > + for (i = 0; i < vq->vring_packed.num; i++) { > > + if (!vq->desc_state_packed[i].data) > > + continue; > > + /* detach_buf clears data, so grab it now. */ > > + buf = vq->desc_state_packed[i].data; > > + detach_buf_packed(vq, i, NULL); > > + END_USE(vq); > > + return buf; > > + } > > + /* That should have freed everything. */ > > + BUG_ON(vq->vq.num_free != vq->vring_packed.num); > > + > > + END_USE(vq); > > return NULL; > > } > > > > @@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) : > > virtqueue_poll_split(_vq, last_used_idx); > > } > > Possible optimization for when dma API is in use: Got it. Will give it a try! Best regards, Tiwei Bie > > ---> > > dma: detecting nop unmap > > drivers need to maintain the dma address for unmap purposes, > but these cycles are wasted when unmap callback is not > defined. Add an API for drivers to check that and avoid > unmap completely. Debug builds still have unmap. > > Signed-off-by: Michael S. Tsirkin > > ---- > > diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h > index a785f2507159..38b2c27c8449 100644 > --- a/include/linux/dma-debug.h > +++ b/include/linux/dma-debug.h > @@ -42,6 +42,11 @@ extern void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); > extern void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > size_t size, int direction, bool map_single); > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return true; > +} > + > extern void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction); > > @@ -121,6 +126,11 @@ static inline void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > { > } > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return false; > +} > + > static inline void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction) > { > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 1db6a6b46d0d..656f3e518166 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -241,6 +241,14 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr, > return addr; > } > > +static inline bool has_dma_unmap(struct device *dev) > +{ > + const struct dma_map_ops *ops = get_dma_ops(dev); > + > + return ops->unmap_page || ops->unmap_sg || ops->unmap_resource || > + has_dma_unmap(dev); > +} > + > static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr, > size_t size, > enum dma_data_direction dir, From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tiwei Bie Subject: Re: [PATCH net-next v2 3/5] virtio_ring: add packed ring support Date: Mon, 10 Sep 2018 10:03:29 +0800 Message-ID: <20180910020329.GA9076@debian> References: <20180711022711.7090-1-tiwei.bie@intel.com> <20180711022711.7090-4-tiwei.bie@intel.com> <20180907083500-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: virtio-dev@lists.oasis-open.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, wexu@redhat.com To: "Michael S. Tsirkin" Return-path: Content-Disposition: inline In-Reply-To: <20180907083500-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org On Fri, Sep 07, 2018 at 09:49:14AM -0400, Michael S. Tsirkin wrote: > On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie wrote: > > This commit introduces the support (without EVENT_IDX) for > > packed ring. > > > > Signed-off-by: Tiwei Bie > > --- > > drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++- > > 1 file changed, 487 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index c4f8abc7445a..f317b485ba54 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -55,12 +55,21 @@ > > #define END_USE(vq) > > #endif > > > > +#define _VRING_DESC_F_AVAIL(b) ((__u16)(b) << 7) > > +#define _VRING_DESC_F_USED(b) ((__u16)(b) << 15) > > Underscore followed by an upper case letter isn't a good idea > for a symbol. And it's not nice that this does not > use the VRING_DESC_F_USED from the header. > How about ((b) ? VRING_DESC_F_USED : 0) instead? > Is produced code worse then? Yes, I think the produced code is worse when we use conditional expression. Below is a simple test: #define foo1(b) ((b) << 10) #define foo2(b) ((b) ? (1 << 10) : 0) unsigned short bar(unsigned short b) { return foo1(b); } unsigned short baz(unsigned short b) { return foo2(b); } With `gcc -O3 -S`, I got below assembly code: .file "tmp.c" .text .p2align 4,,15 .globl bar .type bar, @function bar: .LFB0: .cfi_startproc movl %edi, %eax sall $10, %eax ret .cfi_endproc .LFE0: .size bar, .-bar .p2align 4,,15 .globl baz .type baz, @function baz: .LFB1: .cfi_startproc xorl %eax, %eax testw %di, %di setne %al sall $10, %eax ret .cfi_endproc .LFE1: .size baz, .-baz .ident "GCC: (Debian 8.2.0-4) 8.2.0" .section .note.GNU-stack,"",@progbits That is to say, for `((b) << 10)`, it will shift the register directly. But for `((b) ? (1 << 10) : 0)`, in above code, it will zero eax first, and set al to 1 depend on whether di is 0, and shift eax. > > > + > > struct vring_desc_state { > > void *data; /* Data for callback. */ > > struct vring_desc *indir_desc; /* Indirect descriptor, if any. */ > > }; > > > > struct vring_desc_state_packed { > > + void *data; /* Data for callback. */ > > + struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */ > > Include vring_desc_state for these? Sure. > > > + int num; /* Descriptor list length. */ > > + dma_addr_t addr; /* Buffer DMA addr. */ > > + u32 len; /* Buffer length. */ > > + u16 flags; /* Descriptor flags. */ > > This seems only to be used for indirect. Check indirect field above > instead and drop this. The `flags` is also needed to know the direction, i.e. DMA_FROM_DEVICE or DMA_TO_DEVICE when do DMA unmap. > > > int next; /* The next desc state. */ > > Packing things into 16 bit integers will help reduce > cache pressure here. > > Also, this is only used for unmap, so when dma API is not used, > maintaining addr and len list management is unnecessary. How about we > maintain addr/len in a separate array, avoiding accesses on unmap in that case? Sure. I'll give it a try. > > Also, lots of architectures have a nop unmap in the DMA API. > See a proposed patch at the end for optimizing that case. Got it. Thanks. > > > }; > > > > @@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > - virtio_mb(vq->weak_barriers); > > return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx); > > } > > why is this changing the split queue implementation? Because above barrier is also needed by virtqueue_poll_packed(), so I moved it to virtqueue_poll() and also added some comments for it. > > > > > > @@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int num, unsigned long align) > > & ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2; > > } > > > > +static void vring_unmap_state_packed(const struct vring_virtqueue *vq, > > + struct vring_desc_state_packed *state) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = state->flags; > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static void vring_unmap_desc_packed(const struct vring_virtqueue *vq, > > + struct vring_packed_desc *desc) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, desc->flags); > > I see no reason to use virtioXX wrappers for the packed ring. > That's there to support legacy devices. Just use leXX. Okay. > > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue *_vq, > > + unsigned int total_sg, > > + gfp_t gfp) > > +{ > > + struct vring_packed_desc *desc; > > + > > + /* > > + * We require lowmem mappings for the descriptors because > > + * otherwise virt_to_phys will give us bogus addresses in the > > + * virtqueue. > > Where is virt_to_phys used? I don't see it in this patch. In vring_map_single(), virt_to_phys() will be used to translate the address to phys if dma api isn't used: https://github.com/torvalds/linux/blob/a49a9dcce802/drivers/virtio/virtio_ring.c#L197 > > > + */ > > + gfp &= ~__GFP_HIGHMEM; > > + > > + desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp); > > + > > + return desc; > > +} > > + > > static inline int virtqueue_add_packed(struct virtqueue *_vq, > > struct scatterlist *sgs[], > > unsigned int total_sg, > > @@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > void *ctx, > > gfp_t gfp) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + struct vring_packed_desc *desc; > > + struct scatterlist *sg; > > + unsigned int i, n, descs_used, uninitialized_var(prev), err_idx; > > + __virtio16 uninitialized_var(head_flags), flags; > > + u16 head, avail_wrap_counter, id, curr; > > + bool indirect; > > + > > + START_USE(vq); > > + > > + BUG_ON(data == NULL); > > + BUG_ON(ctx && vq->indirect); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return -EIO; > > + } > > + > > +#ifdef DEBUG > > + { > > + ktime_t now = ktime_get(); > > + > > + /* No kick or get, with .1 second between? Warn. */ > > + if (vq->last_add_time_valid) > > + WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time)) > > + > 100); > > + vq->last_add_time = now; > > + vq->last_add_time_valid = true; > > + } > > +#endif > > Add incline helpers for this debug stuff rather than > duplicate it from split ring? Sure. I'd like to do that. > > > > + > > + BUG_ON(total_sg == 0); > > + > > + head = vq->next_avail_idx; > > + avail_wrap_counter = vq->avail_wrap_counter; > > + > > + if (virtqueue_use_indirect(_vq, total_sg)) > > + desc = alloc_indirect_packed(_vq, total_sg, gfp); > > + else { > > + desc = NULL; > > + WARN_ON_ONCE(total_sg > vq->vring_packed.num && !vq->indirect); > > + } > > > Apparently this attempts to treat indirect descriptors same as > direct ones. This is how it is in the split ring, but not in > the packed one. I think you want two separate functions, for > direct and indirect. Okay, I'll do that. > > > + > > + if (desc) { > > + /* Use a single buffer which doesn't continue */ > > + indirect = true; > > + /* Set up rest to use this indirect table. */ > > + i = 0; > > + descs_used = 1; > > + } else { > > + indirect = false; > > + desc = vq->vring_packed.desc; > > + i = head; > > + descs_used = total_sg; > > + } > > + > > + if (vq->vq.num_free < descs_used) { > > + pr_debug("Can't add buf len %i - avail = %i\n", > > + descs_used, vq->vq.num_free); > > + /* FIXME: for historical reasons, we force a notify here if > > + * there are outgoing parts to the buffer. Presumably the > > + * host should service the ring ASAP. */ > > + if (out_sgs) > > + vq->notify(&vq->vq); > > + if (indirect) > > + kfree(desc); > > + END_USE(vq); > > + return -ENOSPC; > > + } > > + > > + id = vq->free_head; > > + BUG_ON(id == vq->vring_packed.num); > > + > > + curr = id; > > + for (n = 0; n < out_sgs + in_sgs; n++) { > > + for (sg = sgs[n]; sg; sg = sg_next(sg)) { > > + dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ? > > + DMA_TO_DEVICE : DMA_FROM_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | > > + (n < out_sgs ? 0 : VRING_DESC_F_WRITE) | > > + _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) | > > + _VRING_DESC_F_USED(!vq->avail_wrap_counter)); > > Spec says: > The VIRTQ_DESC_F_WRITE flags bit is the only valid flag for descriptors in the > indirect table. > > All this logic isn't needed for indirect. > > Also, why re-calculate avail/used flags every time? They only change > when you wrap around. Will do that. Thanks. > > > > + if (!indirect && i == head) > > + head_flags = flags; > > + else > > + desc[i].flags = flags; > > + > > + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); > > + desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length); > > + i++; > > + if (!indirect) { > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[curr].addr = addr; > > + vq->desc_state_packed[curr].len = > > + sg->length; > > + vq->desc_state_packed[curr].flags = > > + virtio16_to_cpu(_vq->vdev, > > + flags); > > + } > > + curr = vq->desc_state_packed[curr].next; > > + > > + if (i >= vq->vring_packed.num) { > > + i = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + } > > + } > > + } > > + > > + prev = (i > 0 ? i : vq->vring_packed.num) - 1; > > + desc[prev].id = cpu_to_virtio16(_vq->vdev, id); > > Is it easier to write this out in all descriptors, to avoid the need to > calculate prev? Yeah, I'll do that. > > > + > > + /* Last one doesn't continue. */ > > + if (total_sg == 1) > > + head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > > + else > > + desc[prev].flags &= cpu_to_virtio16(_vq->vdev, > > + ~VRING_DESC_F_NEXT); > > Wouldn't it be easier to avoid setting VRING_DESC_F_NEXT > in the first place? > if (n != in_sgs - 1 && n != out_sgs - 1) Will this affect the branch prediction? > > must be better than writing descriptor an extra time. Not quite sure about this. I think this descriptor has just been written, it should still be in the cache. > > > + > > + if (indirect) { > > + /* Now that the indirect table is filled in, map it. */ > > + dma_addr_t addr = vring_map_single( > > + vq, desc, total_sg * sizeof(struct vring_packed_desc), > > + DMA_TO_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT | > > + _VRING_DESC_F_AVAIL(avail_wrap_counter) | > > + _VRING_DESC_F_USED(!avail_wrap_counter)); > > + vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev, > > + addr); > > + vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev, > > + total_sg * sizeof(struct vring_packed_desc)); > > + vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id); > > + > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[id].addr = addr; > > + vq->desc_state_packed[id].len = total_sg * > > + sizeof(struct vring_packed_desc); > > + vq->desc_state_packed[id].flags = > > + virtio16_to_cpu(_vq->vdev, head_flags); > > + } > > + } > > + > > + /* We're using some buffers from the free list. */ > > + vq->vq.num_free -= descs_used; > > + > > + /* Update free pointer */ > > + if (indirect) { > > + n = head + 1; > > + if (n >= vq->vring_packed.num) { > > + n = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + vq->next_avail_idx = n; > > + vq->free_head = vq->desc_state_packed[id].next; > > + } else { > > + vq->next_avail_idx = i; > > + vq->free_head = curr; > > + } > > + > > + /* Store token and indirect buffer state. */ > > + vq->desc_state_packed[id].num = descs_used; > > + vq->desc_state_packed[id].data = data; > > + if (indirect) > > + vq->desc_state_packed[id].indir_desc = desc; > > + else > > + vq->desc_state_packed[id].indir_desc = ctx; > > + > > + /* A driver MUST NOT make the first descriptor in the list > > + * available before all subsequent descriptors comprising > > + * the list are made available. */ > > + virtio_wmb(vq->weak_barriers); > > + vq->vring_packed.desc[head].flags = head_flags; > > + vq->num_added += descs_used; > > + > > + pr_debug("Added buffer head %i to %p\n", head, vq); > > + END_USE(vq); > > + > > + return 0; > > + > > +unmap_release: > > + err_idx = i; > > + i = head; > > + > > + for (n = 0; n < total_sg; n++) { > > + if (i == err_idx) > > + break; > > + vring_unmap_desc_packed(vq, &desc[i]); > > + i++; > > + if (!indirect && i >= vq->vring_packed.num) > > + i = 0; > > + } > > + > > + vq->avail_wrap_counter = avail_wrap_counter; > > + > > + if (indirect) > > + kfree(desc); > > + > > + END_USE(vq); > > return -EIO; > > } > > > > static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 flags; > > + bool needs_kick; > > + u32 snapshot; > > + > > + START_USE(vq); > > + /* We need to expose the new flags value before checking notification > > + * suppressions. */ > > + virtio_mb(vq->weak_barriers); > > + > > + snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); > > + flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; > > What are all these hard-coded things? Also either we do READ_ONCE > everywhere or nowhere. Why is this place special? Any why read 32 bit > if you only want the 16? Yeah, READ_ONCE() and reading 32bits are not really needed in this patch. But it's needed in the next patch. I thought it's not wrong to do this, so I introduced them from the first place. Just to double check: is the below code (apart from the hard-coded value and virtio16) from the next patch OK? """ snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); + off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff)); flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; """ > > And doesn't sparse complain about cast to __virtio16? I'll give it a try in the next version. > > > + > > +#ifdef DEBUG > > + if (vq->last_add_time_valid) { > > + WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), > > + vq->last_add_time)) > 100); > > + } > > + vq->last_add_time_valid = false; > > +#endif > > + > > + needs_kick = (flags != VRING_EVENT_F_DISABLE); > > + END_USE(vq); > > + return needs_kick; > > +} > > + > > +static void detach_buf_packed(struct vring_virtqueue *vq, > > + unsigned int id, void **ctx) > > +{ > > + struct vring_desc_state_packed *state = NULL; > > + struct vring_packed_desc *desc; > > + unsigned int curr, i; > > + > > + /* Clear data ptr. */ > > + vq->desc_state_packed[id].data = NULL; > > + > > + curr = id; > > + for (i = 0; i < vq->desc_state_packed[id].num; i++) { > > + state = &vq->desc_state_packed[curr]; > > + vring_unmap_state_packed(vq, state); > > + curr = state->next; > > + } > > + > > + BUG_ON(state == NULL); > > + vq->vq.num_free += vq->desc_state_packed[id].num; > > + state->next = vq->free_head; > > + vq->free_head = id; > > + > > + if (vq->indirect) { > > + u32 len; > > + > > + /* Free the indirect table, if any, now that it's unmapped. */ > > + desc = vq->desc_state_packed[id].indir_desc; > > + if (!desc) > > + return; > > + > > + if (vring_use_dma_api(vq->vq.vdev)) { > > + len = vq->desc_state_packed[id].len; > > + for (i = 0; i < len / sizeof(struct vring_packed_desc); > > + i++) > > + vring_unmap_desc_packed(vq, &desc[i]); > > + } > > + kfree(desc); > > + vq->desc_state_packed[id].indir_desc = NULL; > > + } else if (ctx) { > > + *ctx = vq->desc_state_packed[id].indir_desc; > > + } > > +} > > + > > +static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > > + u16 idx, bool used_wrap_counter) > > +{ > > + u16 flags; > > + bool avail, used; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, > > + vq->vring_packed.desc[idx].flags); > > + avail = !!(flags & VRING_DESC_F_AVAIL); > > + used = !!(flags & VRING_DESC_F_USED); > > + > > + return avail == used && used == used_wrap_counter; > > I think that you don't need to look at avail flag to detect a used > descriptor. The reason device writes it is to avoid confusing > *device* next time descriptor wraps. Okay, I'll just check the used flag. > > > } > > > > static inline bool more_used_packed(const struct vring_virtqueue *vq) > > { > > - return false; > > + return is_used_desc_packed(vq, vq->last_used_idx, > > + vq->used_wrap_counter); > > } > > > > static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > unsigned int *len, > > void **ctx) > > { > > - return NULL; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 last_used, id; > > + void *ret; > > + > > + START_USE(vq); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return NULL; > > + } > > + > > + if (!more_used_packed(vq)) { > > + pr_debug("No more buffers in queue\n"); > > + END_USE(vq); > > + return NULL; > > + } > > + > > + /* Only get used elements after they have been exposed by host. */ > > + virtio_rmb(vq->weak_barriers); > > + > > + last_used = vq->last_used_idx; > > + id = virtio16_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].id); > > + *len = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].len); > > + > > + if (unlikely(id >= vq->vring_packed.num)) { > > + BAD_RING(vq, "id %u out of range\n", id); > > + return NULL; > > + } > > + if (unlikely(!vq->desc_state_packed[id].data)) { > > + BAD_RING(vq, "id %u is not a head!\n", id); > > + return NULL; > > + } > > + > > + vq->last_used_idx += vq->desc_state_packed[id].num; > > + if (vq->last_used_idx >= vq->vring_packed.num) { > > + vq->last_used_idx -= vq->vring_packed.num; > > + vq->used_wrap_counter ^= 1; > > + } > > + > > + /* detach_buf_packed clears data, so grab it now. */ > > + ret = vq->desc_state_packed[id].data; > > + detach_buf_packed(vq, id, ctx); > > + > > +#ifdef DEBUG > > + vq->last_add_time_valid = false; > > +#endif > > + > > + END_USE(vq); > > + return ret; > > } > > > > static void virtqueue_disable_cb_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_DISABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > } > > > > static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > { > > - return 0; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > + > > + END_USE(vq); > > + return vq->last_used_idx | ((u16)vq->used_wrap_counter << 15); > > } > > > > -static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned last_used_idx) > > +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned off_wrap) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + bool wrap_counter; > > + u16 used_idx; > > + > > + wrap_counter = off_wrap >> 15; > > + used_idx = off_wrap & ~(1 << 15); > > + > > + return is_used_desc_packed(vq, used_idx, wrap_counter); > > These >> 15 << 15 all over the place duplicate info. > Pls put 15 in the header. Sure. > > Also can you maintain the counters properly shifted? > Then just use them. Then, we may need to maintain both of the shifted wrapper counters and un-shifted wrapper counters at the same time. > > > > } > > > > static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > + } > > + > > + if (more_used_packed(vq)) { > > + END_USE(vq); > > + return false; > > + } > > + > > + END_USE(vq); > > + return true; > > } > > > > static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + unsigned int i; > > + void *buf; > > + > > + START_USE(vq); > > + > > + for (i = 0; i < vq->vring_packed.num; i++) { > > + if (!vq->desc_state_packed[i].data) > > + continue; > > + /* detach_buf clears data, so grab it now. */ > > + buf = vq->desc_state_packed[i].data; > > + detach_buf_packed(vq, i, NULL); > > + END_USE(vq); > > + return buf; > > + } > > + /* That should have freed everything. */ > > + BUG_ON(vq->vq.num_free != vq->vring_packed.num); > > + > > + END_USE(vq); > > return NULL; > > } > > > > @@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) : > > virtqueue_poll_split(_vq, last_used_idx); > > } > > Possible optimization for when dma API is in use: Got it. Will give it a try! Best regards, Tiwei Bie > > ---> > > dma: detecting nop unmap > > drivers need to maintain the dma address for unmap purposes, > but these cycles are wasted when unmap callback is not > defined. Add an API for drivers to check that and avoid > unmap completely. Debug builds still have unmap. > > Signed-off-by: Michael S. Tsirkin > > ---- > > diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h > index a785f2507159..38b2c27c8449 100644 > --- a/include/linux/dma-debug.h > +++ b/include/linux/dma-debug.h > @@ -42,6 +42,11 @@ extern void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); > extern void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > size_t size, int direction, bool map_single); > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return true; > +} > + > extern void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction); > > @@ -121,6 +126,11 @@ static inline void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > { > } > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return false; > +} > + > static inline void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction) > { > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 1db6a6b46d0d..656f3e518166 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -241,6 +241,14 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr, > return addr; > } > > +static inline bool has_dma_unmap(struct device *dev) > +{ > + const struct dma_map_ops *ops = get_dma_ops(dev); > + > + return ops->unmap_page || ops->unmap_sg || ops->unmap_resource || > + has_dma_unmap(dev); > +} > + > static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr, > size_t size, > enum dma_data_direction dir, From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-4826-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 2CA11985C96 for ; Mon, 10 Sep 2018 02:04:34 +0000 (UTC) Date: Mon, 10 Sep 2018 10:03:29 +0800 From: Tiwei Bie Message-ID: <20180910020329.GA9076@debian> References: <20180711022711.7090-1-tiwei.bie@intel.com> <20180711022711.7090-4-tiwei.bie@intel.com> <20180907083500-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180907083500-mutt-send-email-mst@kernel.org> Subject: [virtio-dev] Re: [PATCH net-next v2 3/5] virtio_ring: add packed ring support To: "Michael S. Tsirkin" Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, virtio-dev@lists.oasis-open.org, wexu@redhat.com, jfreimann@redhat.com List-ID: On Fri, Sep 07, 2018 at 09:49:14AM -0400, Michael S. Tsirkin wrote: > On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie wrote: > > This commit introduces the support (without EVENT_IDX) for > > packed ring. > > > > Signed-off-by: Tiwei Bie > > --- > > drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++- > > 1 file changed, 487 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index c4f8abc7445a..f317b485ba54 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -55,12 +55,21 @@ > > #define END_USE(vq) > > #endif > > > > +#define _VRING_DESC_F_AVAIL(b) ((__u16)(b) << 7) > > +#define _VRING_DESC_F_USED(b) ((__u16)(b) << 15) > > Underscore followed by an upper case letter isn't a good idea > for a symbol. And it's not nice that this does not > use the VRING_DESC_F_USED from the header. > How about ((b) ? VRING_DESC_F_USED : 0) instead? > Is produced code worse then? Yes, I think the produced code is worse when we use conditional expression. Below is a simple test: #define foo1(b) ((b) << 10) #define foo2(b) ((b) ? (1 << 10) : 0) unsigned short bar(unsigned short b) { return foo1(b); } unsigned short baz(unsigned short b) { return foo2(b); } With `gcc -O3 -S`, I got below assembly code: .file "tmp.c" .text .p2align 4,,15 .globl bar .type bar, @function bar: .LFB0: .cfi_startproc movl %edi, %eax sall $10, %eax ret .cfi_endproc .LFE0: .size bar, .-bar .p2align 4,,15 .globl baz .type baz, @function baz: .LFB1: .cfi_startproc xorl %eax, %eax testw %di, %di setne %al sall $10, %eax ret .cfi_endproc .LFE1: .size baz, .-baz .ident "GCC: (Debian 8.2.0-4) 8.2.0" .section .note.GNU-stack,"",@progbits That is to say, for `((b) << 10)`, it will shift the register directly. But for `((b) ? (1 << 10) : 0)`, in above code, it will zero eax first, and set al to 1 depend on whether di is 0, and shift eax. > > > + > > struct vring_desc_state { > > void *data; /* Data for callback. */ > > struct vring_desc *indir_desc; /* Indirect descriptor, if any. */ > > }; > > > > struct vring_desc_state_packed { > > + void *data; /* Data for callback. */ > > + struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */ > > Include vring_desc_state for these? Sure. > > > + int num; /* Descriptor list length. */ > > + dma_addr_t addr; /* Buffer DMA addr. */ > > + u32 len; /* Buffer length. */ > > + u16 flags; /* Descriptor flags. */ > > This seems only to be used for indirect. Check indirect field above > instead and drop this. The `flags` is also needed to know the direction, i.e. DMA_FROM_DEVICE or DMA_TO_DEVICE when do DMA unmap. > > > int next; /* The next desc state. */ > > Packing things into 16 bit integers will help reduce > cache pressure here. > > Also, this is only used for unmap, so when dma API is not used, > maintaining addr and len list management is unnecessary. How about we > maintain addr/len in a separate array, avoiding accesses on unmap in that case? Sure. I'll give it a try. > > Also, lots of architectures have a nop unmap in the DMA API. > See a proposed patch at the end for optimizing that case. Got it. Thanks. > > > }; > > > > @@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > - virtio_mb(vq->weak_barriers); > > return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx); > > } > > why is this changing the split queue implementation? Because above barrier is also needed by virtqueue_poll_packed(), so I moved it to virtqueue_poll() and also added some comments for it. > > > > > > @@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int num, unsigned long align) > > & ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2; > > } > > > > +static void vring_unmap_state_packed(const struct vring_virtqueue *vq, > > + struct vring_desc_state_packed *state) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = state->flags; > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + state->addr, state->len, > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static void vring_unmap_desc_packed(const struct vring_virtqueue *vq, > > + struct vring_packed_desc *desc) > > +{ > > + u16 flags; > > + > > + if (!vring_use_dma_api(vq->vq.vdev)) > > + return; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, desc->flags); > > I see no reason to use virtioXX wrappers for the packed ring. > That's there to support legacy devices. Just use leXX. Okay. > > > + > > + if (flags & VRING_DESC_F_INDIRECT) { > > + dma_unmap_single(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } else { > > + dma_unmap_page(vring_dma_dev(vq), > > + virtio64_to_cpu(vq->vq.vdev, desc->addr), > > + virtio32_to_cpu(vq->vq.vdev, desc->len), > > + (flags & VRING_DESC_F_WRITE) ? > > + DMA_FROM_DEVICE : DMA_TO_DEVICE); > > + } > > +} > > + > > +static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue *_vq, > > + unsigned int total_sg, > > + gfp_t gfp) > > +{ > > + struct vring_packed_desc *desc; > > + > > + /* > > + * We require lowmem mappings for the descriptors because > > + * otherwise virt_to_phys will give us bogus addresses in the > > + * virtqueue. > > Where is virt_to_phys used? I don't see it in this patch. In vring_map_single(), virt_to_phys() will be used to translate the address to phys if dma api isn't used: https://github.com/torvalds/linux/blob/a49a9dcce802/drivers/virtio/virtio_ring.c#L197 > > > + */ > > + gfp &= ~__GFP_HIGHMEM; > > + > > + desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp); > > + > > + return desc; > > +} > > + > > static inline int virtqueue_add_packed(struct virtqueue *_vq, > > struct scatterlist *sgs[], > > unsigned int total_sg, > > @@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > void *ctx, > > gfp_t gfp) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + struct vring_packed_desc *desc; > > + struct scatterlist *sg; > > + unsigned int i, n, descs_used, uninitialized_var(prev), err_idx; > > + __virtio16 uninitialized_var(head_flags), flags; > > + u16 head, avail_wrap_counter, id, curr; > > + bool indirect; > > + > > + START_USE(vq); > > + > > + BUG_ON(data == NULL); > > + BUG_ON(ctx && vq->indirect); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return -EIO; > > + } > > + > > +#ifdef DEBUG > > + { > > + ktime_t now = ktime_get(); > > + > > + /* No kick or get, with .1 second between? Warn. */ > > + if (vq->last_add_time_valid) > > + WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time)) > > + > 100); > > + vq->last_add_time = now; > > + vq->last_add_time_valid = true; > > + } > > +#endif > > Add incline helpers for this debug stuff rather than > duplicate it from split ring? Sure. I'd like to do that. > > > > + > > + BUG_ON(total_sg == 0); > > + > > + head = vq->next_avail_idx; > > + avail_wrap_counter = vq->avail_wrap_counter; > > + > > + if (virtqueue_use_indirect(_vq, total_sg)) > > + desc = alloc_indirect_packed(_vq, total_sg, gfp); > > + else { > > + desc = NULL; > > + WARN_ON_ONCE(total_sg > vq->vring_packed.num && !vq->indirect); > > + } > > > Apparently this attempts to treat indirect descriptors same as > direct ones. This is how it is in the split ring, but not in > the packed one. I think you want two separate functions, for > direct and indirect. Okay, I'll do that. > > > + > > + if (desc) { > > + /* Use a single buffer which doesn't continue */ > > + indirect = true; > > + /* Set up rest to use this indirect table. */ > > + i = 0; > > + descs_used = 1; > > + } else { > > + indirect = false; > > + desc = vq->vring_packed.desc; > > + i = head; > > + descs_used = total_sg; > > + } > > + > > + if (vq->vq.num_free < descs_used) { > > + pr_debug("Can't add buf len %i - avail = %i\n", > > + descs_used, vq->vq.num_free); > > + /* FIXME: for historical reasons, we force a notify here if > > + * there are outgoing parts to the buffer. Presumably the > > + * host should service the ring ASAP. */ > > + if (out_sgs) > > + vq->notify(&vq->vq); > > + if (indirect) > > + kfree(desc); > > + END_USE(vq); > > + return -ENOSPC; > > + } > > + > > + id = vq->free_head; > > + BUG_ON(id == vq->vring_packed.num); > > + > > + curr = id; > > + for (n = 0; n < out_sgs + in_sgs; n++) { > > + for (sg = sgs[n]; sg; sg = sg_next(sg)) { > > + dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ? > > + DMA_TO_DEVICE : DMA_FROM_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | > > + (n < out_sgs ? 0 : VRING_DESC_F_WRITE) | > > + _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) | > > + _VRING_DESC_F_USED(!vq->avail_wrap_counter)); > > Spec says: > The VIRTQ_DESC_F_WRITE flags bit is the only valid flag for descriptors in the > indirect table. > > All this logic isn't needed for indirect. > > Also, why re-calculate avail/used flags every time? They only change > when you wrap around. Will do that. Thanks. > > > > + if (!indirect && i == head) > > + head_flags = flags; > > + else > > + desc[i].flags = flags; > > + > > + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); > > + desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length); > > + i++; > > + if (!indirect) { > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[curr].addr = addr; > > + vq->desc_state_packed[curr].len = > > + sg->length; > > + vq->desc_state_packed[curr].flags = > > + virtio16_to_cpu(_vq->vdev, > > + flags); > > + } > > + curr = vq->desc_state_packed[curr].next; > > + > > + if (i >= vq->vring_packed.num) { > > + i = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + } > > + } > > + } > > + > > + prev = (i > 0 ? i : vq->vring_packed.num) - 1; > > + desc[prev].id = cpu_to_virtio16(_vq->vdev, id); > > Is it easier to write this out in all descriptors, to avoid the need to > calculate prev? Yeah, I'll do that. > > > + > > + /* Last one doesn't continue. */ > > + if (total_sg == 1) > > + head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > > + else > > + desc[prev].flags &= cpu_to_virtio16(_vq->vdev, > > + ~VRING_DESC_F_NEXT); > > Wouldn't it be easier to avoid setting VRING_DESC_F_NEXT > in the first place? > if (n != in_sgs - 1 && n != out_sgs - 1) Will this affect the branch prediction? > > must be better than writing descriptor an extra time. Not quite sure about this. I think this descriptor has just been written, it should still be in the cache. > > > + > > + if (indirect) { > > + /* Now that the indirect table is filled in, map it. */ > > + dma_addr_t addr = vring_map_single( > > + vq, desc, total_sg * sizeof(struct vring_packed_desc), > > + DMA_TO_DEVICE); > > + if (vring_mapping_error(vq, addr)) > > + goto unmap_release; > > + > > + head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT | > > + _VRING_DESC_F_AVAIL(avail_wrap_counter) | > > + _VRING_DESC_F_USED(!avail_wrap_counter)); > > + vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev, > > + addr); > > + vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev, > > + total_sg * sizeof(struct vring_packed_desc)); > > + vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id); > > + > > + if (vring_use_dma_api(_vq->vdev)) { > > + vq->desc_state_packed[id].addr = addr; > > + vq->desc_state_packed[id].len = total_sg * > > + sizeof(struct vring_packed_desc); > > + vq->desc_state_packed[id].flags = > > + virtio16_to_cpu(_vq->vdev, head_flags); > > + } > > + } > > + > > + /* We're using some buffers from the free list. */ > > + vq->vq.num_free -= descs_used; > > + > > + /* Update free pointer */ > > + if (indirect) { > > + n = head + 1; > > + if (n >= vq->vring_packed.num) { > > + n = 0; > > + vq->avail_wrap_counter ^= 1; > > + } > > + vq->next_avail_idx = n; > > + vq->free_head = vq->desc_state_packed[id].next; > > + } else { > > + vq->next_avail_idx = i; > > + vq->free_head = curr; > > + } > > + > > + /* Store token and indirect buffer state. */ > > + vq->desc_state_packed[id].num = descs_used; > > + vq->desc_state_packed[id].data = data; > > + if (indirect) > > + vq->desc_state_packed[id].indir_desc = desc; > > + else > > + vq->desc_state_packed[id].indir_desc = ctx; > > + > > + /* A driver MUST NOT make the first descriptor in the list > > + * available before all subsequent descriptors comprising > > + * the list are made available. */ > > + virtio_wmb(vq->weak_barriers); > > + vq->vring_packed.desc[head].flags = head_flags; > > + vq->num_added += descs_used; > > + > > + pr_debug("Added buffer head %i to %p\n", head, vq); > > + END_USE(vq); > > + > > + return 0; > > + > > +unmap_release: > > + err_idx = i; > > + i = head; > > + > > + for (n = 0; n < total_sg; n++) { > > + if (i == err_idx) > > + break; > > + vring_unmap_desc_packed(vq, &desc[i]); > > + i++; > > + if (!indirect && i >= vq->vring_packed.num) > > + i = 0; > > + } > > + > > + vq->avail_wrap_counter = avail_wrap_counter; > > + > > + if (indirect) > > + kfree(desc); > > + > > + END_USE(vq); > > return -EIO; > > } > > > > static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 flags; > > + bool needs_kick; > > + u32 snapshot; > > + > > + START_USE(vq); > > + /* We need to expose the new flags value before checking notification > > + * suppressions. */ > > + virtio_mb(vq->weak_barriers); > > + > > + snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); > > + flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; > > What are all these hard-coded things? Also either we do READ_ONCE > everywhere or nowhere. Why is this place special? Any why read 32 bit > if you only want the 16? Yeah, READ_ONCE() and reading 32bits are not really needed in this patch. But it's needed in the next patch. I thought it's not wrong to do this, so I introduced them from the first place. Just to double check: is the below code (apart from the hard-coded value and virtio16) from the next patch OK? """ snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device); + off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff)); flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3; """ > > And doesn't sparse complain about cast to __virtio16? I'll give it a try in the next version. > > > + > > +#ifdef DEBUG > > + if (vq->last_add_time_valid) { > > + WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), > > + vq->last_add_time)) > 100); > > + } > > + vq->last_add_time_valid = false; > > +#endif > > + > > + needs_kick = (flags != VRING_EVENT_F_DISABLE); > > + END_USE(vq); > > + return needs_kick; > > +} > > + > > +static void detach_buf_packed(struct vring_virtqueue *vq, > > + unsigned int id, void **ctx) > > +{ > > + struct vring_desc_state_packed *state = NULL; > > + struct vring_packed_desc *desc; > > + unsigned int curr, i; > > + > > + /* Clear data ptr. */ > > + vq->desc_state_packed[id].data = NULL; > > + > > + curr = id; > > + for (i = 0; i < vq->desc_state_packed[id].num; i++) { > > + state = &vq->desc_state_packed[curr]; > > + vring_unmap_state_packed(vq, state); > > + curr = state->next; > > + } > > + > > + BUG_ON(state == NULL); > > + vq->vq.num_free += vq->desc_state_packed[id].num; > > + state->next = vq->free_head; > > + vq->free_head = id; > > + > > + if (vq->indirect) { > > + u32 len; > > + > > + /* Free the indirect table, if any, now that it's unmapped. */ > > + desc = vq->desc_state_packed[id].indir_desc; > > + if (!desc) > > + return; > > + > > + if (vring_use_dma_api(vq->vq.vdev)) { > > + len = vq->desc_state_packed[id].len; > > + for (i = 0; i < len / sizeof(struct vring_packed_desc); > > + i++) > > + vring_unmap_desc_packed(vq, &desc[i]); > > + } > > + kfree(desc); > > + vq->desc_state_packed[id].indir_desc = NULL; > > + } else if (ctx) { > > + *ctx = vq->desc_state_packed[id].indir_desc; > > + } > > +} > > + > > +static inline bool is_used_desc_packed(const struct vring_virtqueue *vq, > > + u16 idx, bool used_wrap_counter) > > +{ > > + u16 flags; > > + bool avail, used; > > + > > + flags = virtio16_to_cpu(vq->vq.vdev, > > + vq->vring_packed.desc[idx].flags); > > + avail = !!(flags & VRING_DESC_F_AVAIL); > > + used = !!(flags & VRING_DESC_F_USED); > > + > > + return avail == used && used == used_wrap_counter; > > I think that you don't need to look at avail flag to detect a used > descriptor. The reason device writes it is to avoid confusing > *device* next time descriptor wraps. Okay, I'll just check the used flag. > > > } > > > > static inline bool more_used_packed(const struct vring_virtqueue *vq) > > { > > - return false; > > + return is_used_desc_packed(vq, vq->last_used_idx, > > + vq->used_wrap_counter); > > } > > > > static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > > unsigned int *len, > > void **ctx) > > { > > - return NULL; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + u16 last_used, id; > > + void *ret; > > + > > + START_USE(vq); > > + > > + if (unlikely(vq->broken)) { > > + END_USE(vq); > > + return NULL; > > + } > > + > > + if (!more_used_packed(vq)) { > > + pr_debug("No more buffers in queue\n"); > > + END_USE(vq); > > + return NULL; > > + } > > + > > + /* Only get used elements after they have been exposed by host. */ > > + virtio_rmb(vq->weak_barriers); > > + > > + last_used = vq->last_used_idx; > > + id = virtio16_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].id); > > + *len = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].len); > > + > > + if (unlikely(id >= vq->vring_packed.num)) { > > + BAD_RING(vq, "id %u out of range\n", id); > > + return NULL; > > + } > > + if (unlikely(!vq->desc_state_packed[id].data)) { > > + BAD_RING(vq, "id %u is not a head!\n", id); > > + return NULL; > > + } > > + > > + vq->last_used_idx += vq->desc_state_packed[id].num; > > + if (vq->last_used_idx >= vq->vring_packed.num) { > > + vq->last_used_idx -= vq->vring_packed.num; > > + vq->used_wrap_counter ^= 1; > > + } > > + > > + /* detach_buf_packed clears data, so grab it now. */ > > + ret = vq->desc_state_packed[id].data; > > + detach_buf_packed(vq, id, ctx); > > + > > +#ifdef DEBUG > > + vq->last_add_time_valid = false; > > +#endif > > + > > + END_USE(vq); > > + return ret; > > } > > > > static void virtqueue_disable_cb_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_DISABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > } > > > > static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq) > > { > > - return 0; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + } > > + > > + END_USE(vq); > > + return vq->last_used_idx | ((u16)vq->used_wrap_counter << 15); > > } > > > > -static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned last_used_idx) > > +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned off_wrap) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + bool wrap_counter; > > + u16 used_idx; > > + > > + wrap_counter = off_wrap >> 15; > > + used_idx = off_wrap & ~(1 << 15); > > + > > + return is_used_desc_packed(vq, used_idx, wrap_counter); > > These >> 15 << 15 all over the place duplicate info. > Pls put 15 in the header. Sure. > > Also can you maintain the counters properly shifted? > Then just use them. Then, we may need to maintain both of the shifted wrapper counters and un-shifted wrapper counters at the same time. > > > > } > > > > static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq) > > { > > - return false; > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + > > + START_USE(vq); > > + > > + /* We optimistically turn back on interrupts, then check if there was > > + * more to do. */ > > + > > + if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) { > > + vq->event_flags_shadow = VRING_EVENT_F_ENABLE; > > + vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev, > > + vq->event_flags_shadow); > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > + } > > + > > + if (more_used_packed(vq)) { > > + END_USE(vq); > > + return false; > > + } > > + > > + END_USE(vq); > > + return true; > > } > > > > static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq) > > { > > + struct vring_virtqueue *vq = to_vvq(_vq); > > + unsigned int i; > > + void *buf; > > + > > + START_USE(vq); > > + > > + for (i = 0; i < vq->vring_packed.num; i++) { > > + if (!vq->desc_state_packed[i].data) > > + continue; > > + /* detach_buf clears data, so grab it now. */ > > + buf = vq->desc_state_packed[i].data; > > + detach_buf_packed(vq, i, NULL); > > + END_USE(vq); > > + return buf; > > + } > > + /* That should have freed everything. */ > > + BUG_ON(vq->vq.num_free != vq->vring_packed.num); > > + > > + END_USE(vq); > > return NULL; > > } > > > > @@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > + /* We need to enable interrupts first before re-checking > > + * for more used buffers. */ > > + virtio_mb(vq->weak_barriers); > > return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) : > > virtqueue_poll_split(_vq, last_used_idx); > > } > > Possible optimization for when dma API is in use: Got it. Will give it a try! Best regards, Tiwei Bie > > ---> > > dma: detecting nop unmap > > drivers need to maintain the dma address for unmap purposes, > but these cycles are wasted when unmap callback is not > defined. Add an API for drivers to check that and avoid > unmap completely. Debug builds still have unmap. > > Signed-off-by: Michael S. Tsirkin > > ---- > > diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h > index a785f2507159..38b2c27c8449 100644 > --- a/include/linux/dma-debug.h > +++ b/include/linux/dma-debug.h > @@ -42,6 +42,11 @@ extern void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); > extern void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > size_t size, int direction, bool map_single); > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return true; > +} > + > extern void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction); > > @@ -121,6 +126,11 @@ static inline void debug_dma_unmap_page(struct device *dev, dma_addr_t addr, > { > } > > +static inline bool has_debug_dma_unmap(struct device *dev) > +{ > + return false; > +} > + > static inline void debug_dma_map_sg(struct device *dev, struct scatterlist *sg, > int nents, int mapped_ents, int direction) > { > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 1db6a6b46d0d..656f3e518166 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -241,6 +241,14 @@ static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr, > return addr; > } > > +static inline bool has_dma_unmap(struct device *dev) > +{ > + const struct dma_map_ops *ops = get_dma_ops(dev); > + > + return ops->unmap_page || ops->unmap_sg || ops->unmap_resource || > + has_dma_unmap(dev); > +} > + > static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr, > size_t size, > enum dma_data_direction dir, --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org