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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 CC05AC433DF for ; Wed, 3 Jun 2020 07:27:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 987AF2067B for ; Wed, 3 Jun 2020 07:27:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gmafX0bH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726120AbgFCH1w (ORCPT ); Wed, 3 Jun 2020 03:27:52 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:23242 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725867AbgFCH1v (ORCPT ); Wed, 3 Jun 2020 03:27:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591169269; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=P8+F9pTtlr4BDDG3Kk7azmgerG7kStlJicyTK/Y6Eu4=; b=gmafX0bHh23PMDkItxZbrFFa5B7OBsYcLtPWc+zz3SdICVVKGeGPvEuT6DjX+ISitpXjWn sqkQz1czE7iaMtuVXoJg0JZ/cb5xBax0rEPG1Cyol09Wu1s8FLdqBtAF3BUQ3hq2eTb0CW LLzXW5A/KZtfsWAwf+QjKtaGuzOm2Ac= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-117-6k4bs73GNye8e-bXkQh7CQ-1; Wed, 03 Jun 2020 03:27:47 -0400 X-MC-Unique: 6k4bs73GNye8e-bXkQh7CQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A5D21835B40; Wed, 3 Jun 2020 07:27:46 +0000 (UTC) Received: from [10.72.12.214] (ovpn-12-214.pek2.redhat.com [10.72.12.214]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4FDBA10013D6; Wed, 3 Jun 2020 07:27:41 +0000 (UTC) Subject: Re: [PATCH RFC 03/13] vhost: batching fetches To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: =?UTF-8?Q?Eugenio_P=c3=a9rez?= , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org References: <20200602130543.578420-1-mst@redhat.com> <20200602130543.578420-4-mst@redhat.com> From: Jason Wang Message-ID: <3323daa2-19ed-02de-0ff7-ab150f949fff@redhat.com> Date: Wed, 3 Jun 2020 15:27:39 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200602130543.578420-4-mst@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/6/2 下午9:06, Michael S. Tsirkin wrote: > With this patch applied, new and old code perform identically. > > Lots of extra optimizations are now possible, e.g. > we can fetch multiple heads with copy_from/to_user now. > We can get rid of maintaining the log array. Etc etc. > > Signed-off-by: Michael S. Tsirkin > Signed-off-by: Eugenio Pérez > Link: https://lore.kernel.org/r/20200401183118.8334-4-eperezma@redhat.com > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/test.c | 2 +- > drivers/vhost/vhost.c | 47 ++++++++++++++++++++++++++++++++++++++----- > drivers/vhost/vhost.h | 5 ++++- > 3 files changed, 47 insertions(+), 7 deletions(-) > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > index 9a3a09005e03..02806d6f84ef 100644 > --- a/drivers/vhost/test.c > +++ b/drivers/vhost/test.c > @@ -119,7 +119,7 @@ static int vhost_test_open(struct inode *inode, struct file *f) > dev = &n->dev; > vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ]; > n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick; > - vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV, > + vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV + 64, > VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT, NULL); > > f->private_data = n; > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 8f9a07282625..aca2a5b0d078 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -299,6 +299,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > { > vq->num = 1; > vq->ndescs = 0; > + vq->first_desc = 0; > vq->desc = NULL; > vq->avail = NULL; > vq->used = NULL; > @@ -367,6 +368,11 @@ static int vhost_worker(void *data) > return 0; > } > > +static int vhost_vq_num_batch_descs(struct vhost_virtqueue *vq) > +{ > + return vq->max_descs - UIO_MAXIOV; > +} 1 descriptor does not mean 1 iov, e.g userspace may pass several 1 byte length memory regions for us to translate. > + > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) > { > kfree(vq->descs); > @@ -389,6 +395,9 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev) > for (i = 0; i < dev->nvqs; ++i) { > vq = dev->vqs[i]; > vq->max_descs = dev->iov_limit; > + if (vhost_vq_num_batch_descs(vq) < 0) { > + return -EINVAL; > + } > vq->descs = kmalloc_array(vq->max_descs, > sizeof(*vq->descs), > GFP_KERNEL); > @@ -1570,6 +1579,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg > vq->last_avail_idx = s.num; > /* Forget the cached index value. */ > vq->avail_idx = vq->last_avail_idx; > + vq->ndescs = vq->first_desc = 0; > break; > case VHOST_GET_VRING_BASE: > s.index = idx; > @@ -2136,7 +2146,7 @@ static int fetch_indirect_descs(struct vhost_virtqueue *vq, > return 0; > } > > -static int fetch_descs(struct vhost_virtqueue *vq) > +static int fetch_buf(struct vhost_virtqueue *vq) > { > unsigned int i, head, found = 0; > struct vhost_desc *last; > @@ -2149,7 +2159,11 @@ static int fetch_descs(struct vhost_virtqueue *vq) > /* Check it isn't doing very strange things with descriptor numbers. */ > last_avail_idx = vq->last_avail_idx; > > - if (vq->avail_idx == vq->last_avail_idx) { > + if (unlikely(vq->avail_idx == vq->last_avail_idx)) { > + /* If we already have work to do, don't bother re-checking. */ > + if (likely(vq->ndescs)) > + return vq->num; > + > if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) { > vq_err(vq, "Failed to access avail idx at %p\n", > &vq->avail->idx); > @@ -2240,6 +2254,24 @@ static int fetch_descs(struct vhost_virtqueue *vq) > return 0; > } > > +static int fetch_descs(struct vhost_virtqueue *vq) > +{ > + int ret = 0; > + > + if (unlikely(vq->first_desc >= vq->ndescs)) { > + vq->first_desc = 0; > + vq->ndescs = 0; > + } > + > + if (vq->ndescs) > + return 0; > + > + while (!ret && vq->ndescs <= vhost_vq_num_batch_descs(vq)) > + ret = fetch_buf(vq); > + > + return vq->ndescs ? 0 : ret; > +} > + > /* This looks in the virtqueue and for the first available buffer, and converts > * it to an iovec for convenient access. Since descriptors consist of some > * number of output then some number of input descriptors, it's actually two > @@ -2265,7 +2297,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, > if (unlikely(log)) > *log_num = 0; > > - for (i = 0; i < vq->ndescs; ++i) { > + for (i = vq->first_desc; i < vq->ndescs; ++i) { > unsigned iov_count = *in_num + *out_num; > struct vhost_desc *desc = &vq->descs[i]; > int access; > @@ -2311,14 +2343,19 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, > } > > ret = desc->id; > + > + if (!(desc->flags & VRING_DESC_F_NEXT)) > + break; > } > > - vq->ndescs = 0; > + vq->first_desc = i + 1; > > return ret; > > err: > - vhost_discard_vq_desc(vq, 1); > + for (i = vq->first_desc; i < vq->ndescs; ++i) > + if (!(vq->descs[i].flags & VRING_DESC_F_NEXT)) > + vhost_discard_vq_desc(vq, 1); > vq->ndescs = 0; > > return ret; > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 76356edee8e5..a67bda9792ec 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -81,6 +81,7 @@ struct vhost_virtqueue { > > struct vhost_desc *descs; > int ndescs; > + int first_desc; > int max_descs; > > struct file *kick; > @@ -229,7 +230,7 @@ void vhost_iotlb_map_free(struct vhost_iotlb *iotlb, > struct vhost_iotlb_map *map); > > #define vq_err(vq, fmt, ...) do { \ > - pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \ > + pr_err(pr_fmt(fmt), ##__VA_ARGS__); \ Need a separate patch for this? Thanks > if ((vq)->error_ctx) \ > eventfd_signal((vq)->error_ctx, 1);\ > } while (0) > @@ -255,6 +256,8 @@ static inline void vhost_vq_set_backend(struct vhost_virtqueue *vq, > void *private_data) > { > vq->private_data = private_data; > + vq->ndescs = 0; > + vq->first_desc = 0; > } > > /**