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[188.78.141.109]) by smtp.gmail.com with ESMTPSA id w17sm8425820wra.71.2020.06.10.07.29.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jun 2020 07:29:31 -0700 (PDT) Message-ID: <035e82bcf4ade0017641c5b457d0c628c5915732.camel@redhat.com> Subject: Re: [PATCH RFC v7 03/14] vhost: use batched get_vq_desc version From: Eugenio =?ISO-8859-1?Q?P=E9rez?= To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, Jason Wang Date: Wed, 10 Jun 2020 16:29:29 +0200 In-Reply-To: <20200610113515.1497099-4-mst@redhat.com> References: <20200610113515.1497099-1-mst@redhat.com> <20200610113515.1497099-4-mst@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-6.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2020-06-10 at 07:36 -0400, Michael S. Tsirkin wrote: > As testing shows no performance change, switch to that now. > > Signed-off-by: Michael S. Tsirkin > Signed-off-by: Eugenio Pérez > Link: https://lore.kernel.org/r/20200401183118.8334-3-eperezma@redhat.com > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/test.c | 2 +- > drivers/vhost/vhost.c | 318 ++++++++---------------------------------- > drivers/vhost/vhost.h | 7 +- > 3 files changed, 65 insertions(+), 262 deletions(-) > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > index 0466921f4772..7d69778aaa26 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, true, NULL); > > f->private_data = n; > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 11433d709651..28f324fd77df 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -304,6 +304,7 @@ 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; > @@ -372,6 +373,11 @@ 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; > +} > + > static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq) > { > kfree(vq->descs); > @@ -394,6 +400,9 @@ 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); > @@ -1610,6 +1619,7 @@ 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; This is not needed if it is done in vhost_vq_set_backend, as far as I can tell. Actually, maybe it is even better to move `vq->avail_idx = vq->last_avail_idx;` line to vhost_vq_set_backend, it is part of the backend "set up" procedure, isn't it? I tested with virtio_test + batch tests sent in https://lkml.kernel.org/lkml/20200418102217.32327-1-eperezma@redhat.com/T/. I append here what I'm proposing in case it is clearer this way. Thanks! diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 4d198994e7be..809ad2cd2879 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1617,9 +1617,6 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg break; } 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; diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index fed36af5c444..f4902dc808e4 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -258,6 +258,7 @@ static inline void vhost_vq_set_backend(struct vhost_virtqueue *vq, void *private_data) { vq->private_data = private_data; + vq->avail_idx = vq->last_avail_idx; vq->ndescs = 0; vq->first_desc = 0; } > break; > case VHOST_GET_VRING_BASE: > s.index = idx; > @@ -2078,253 +2088,6 @@ static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc) > return next; > } > > -static int get_indirect(struct vhost_virtqueue *vq, > - struct iovec iov[], unsigned int iov_size, > - unsigned int *out_num, unsigned int *in_num, > - struct vhost_log *log, unsigned int *log_num, > - struct vring_desc *indirect) > -{ > - struct vring_desc desc; > - unsigned int i = 0, count, found = 0; > - u32 len = vhost32_to_cpu(vq, indirect->len); > - struct iov_iter from; > - int ret, access; > - > - /* Sanity check */ > - if (unlikely(len % sizeof desc)) { > - vq_err(vq, "Invalid length in indirect descriptor: " > - "len 0x%llx not multiple of 0x%zx\n", > - (unsigned long long)len, > - sizeof desc); > - return -EINVAL; > - } > - > - ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect, > - UIO_MAXIOV, VHOST_ACCESS_RO); > - if (unlikely(ret < 0)) { > - if (ret != -EAGAIN) > - vq_err(vq, "Translation failure %d in indirect.\n", ret); > - return ret; > - } > - iov_iter_init(&from, READ, vq->indirect, ret, len); > - > - /* We will use the result as an address to read from, so most > - * architectures only need a compiler barrier here. */ > - read_barrier_depends(); > - > - count = len / sizeof desc; > - /* Buffers are chained via a 16 bit next field, so > - * we can have at most 2^16 of these. */ > - if (unlikely(count > USHRT_MAX + 1)) { > - vq_err(vq, "Indirect buffer length too big: %d\n", > - indirect->len); > - return -E2BIG; > - } > - > - do { > - unsigned iov_count = *in_num + *out_num; > - if (unlikely(++found > count)) { > - vq_err(vq, "Loop detected: last one at %u " > - "indirect size %u\n", > - i, count); > - return -EINVAL; > - } > - if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) { > - vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n", > - i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc); > - return -EINVAL; > - } > - if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) { > - vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n", > - i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc); > - return -EINVAL; > - } > - > - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) > - access = VHOST_ACCESS_WO; > - else > - access = VHOST_ACCESS_RO; > - > - ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr), > - vhost32_to_cpu(vq, desc.len), iov + iov_count, > - iov_size - iov_count, access); > - if (unlikely(ret < 0)) { > - if (ret != -EAGAIN) > - vq_err(vq, "Translation failure %d indirect idx %d\n", > - ret, i); > - return ret; > - } > - /* If this is an input descriptor, increment that count. */ > - if (access == VHOST_ACCESS_WO) { > - *in_num += ret; > - if (unlikely(log && ret)) { > - log[*log_num].addr = vhost64_to_cpu(vq, desc.addr); > - log[*log_num].len = vhost32_to_cpu(vq, desc.len); > - ++*log_num; > - } > - } else { > - /* If it's an output descriptor, they're all supposed > - * to come before any input descriptors. */ > - if (unlikely(*in_num)) { > - vq_err(vq, "Indirect descriptor " > - "has out after in: idx %d\n", i); > - return -EINVAL; > - } > - *out_num += ret; > - } > - } while ((i = next_desc(vq, &desc)) != -1); > - return 0; > -} > - > -/* 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 > - * iovecs, but we pack them into one and note how many of each there were. > - * > - * This function returns the descriptor number found, or vq->num (which is > - * never a valid descriptor number) if none was found. A negative code is > - * returned on error. */ > -int vhost_get_vq_desc(struct vhost_virtqueue *vq, > - struct iovec iov[], unsigned int iov_size, > - unsigned int *out_num, unsigned int *in_num, > - struct vhost_log *log, unsigned int *log_num) > -{ > - struct vring_desc desc; > - unsigned int i, head, found = 0; > - u16 last_avail_idx; > - __virtio16 avail_idx; > - __virtio16 ring_head; > - int ret, access; > - > - /* 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(vhost_get_avail_idx(vq, &avail_idx))) { > - vq_err(vq, "Failed to access avail idx at %p\n", > - &vq->avail->idx); > - return -EFAULT; > - } > - vq->avail_idx = vhost16_to_cpu(vq, avail_idx); > - > - if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) { > - vq_err(vq, "Guest moved used index from %u to %u", > - last_avail_idx, vq->avail_idx); > - return -EFAULT; > - } > - > - /* If there's nothing new since last we looked, return > - * invalid. > - */ > - if (vq->avail_idx == last_avail_idx) > - return vq->num; > - > - /* Only get avail ring entries after they have been > - * exposed by guest. > - */ > - smp_rmb(); > - } > - > - /* Grab the next descriptor number they're advertising, and increment > - * the index we've seen. */ > - if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) { > - vq_err(vq, "Failed to read head: idx %d address %p\n", > - last_avail_idx, > - &vq->avail->ring[last_avail_idx % vq->num]); > - return -EFAULT; > - } > - > - head = vhost16_to_cpu(vq, ring_head); > - > - /* If their number is silly, that's an error. */ > - if (unlikely(head >= vq->num)) { > - vq_err(vq, "Guest says index %u > %u is available", > - head, vq->num); > - return -EINVAL; > - } > - > - /* When we start there are none of either input nor output. */ > - *out_num = *in_num = 0; > - if (unlikely(log)) > - *log_num = 0; > - > - i = head; > - do { > - unsigned iov_count = *in_num + *out_num; > - if (unlikely(i >= vq->num)) { > - vq_err(vq, "Desc index is %u > %u, head = %u", > - i, vq->num, head); > - return -EINVAL; > - } > - if (unlikely(++found > vq->num)) { > - vq_err(vq, "Loop detected: last one at %u " > - "vq size %u head %u\n", > - i, vq->num, head); > - return -EINVAL; > - } > - ret = vhost_get_desc(vq, &desc, i); > - if (unlikely(ret)) { > - vq_err(vq, "Failed to get descriptor: idx %d addr %p\n", > - i, vq->desc + i); > - return -EFAULT; > - } > - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) { > - ret = get_indirect(vq, iov, iov_size, > - out_num, in_num, > - log, log_num, &desc); > - if (unlikely(ret < 0)) { > - if (ret != -EAGAIN) > - vq_err(vq, "Failure detected " > - "in indirect descriptor at idx %d\n", i); > - return ret; > - } > - continue; > - } > - > - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) > - access = VHOST_ACCESS_WO; > - else > - access = VHOST_ACCESS_RO; > - ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr), > - vhost32_to_cpu(vq, desc.len), iov + iov_count, > - iov_size - iov_count, access); > - if (unlikely(ret < 0)) { > - if (ret != -EAGAIN) > - vq_err(vq, "Translation failure %d descriptor idx %d\n", > - ret, i); > - return ret; > - } > - if (access == VHOST_ACCESS_WO) { > - /* If this is an input descriptor, > - * increment that count. */ > - *in_num += ret; > - if (unlikely(log && ret)) { > - log[*log_num].addr = vhost64_to_cpu(vq, desc.addr); > - log[*log_num].len = vhost32_to_cpu(vq, desc.len); > - ++*log_num; > - } > - } else { > - /* If it's an output descriptor, they're all supposed > - * to come before any input descriptors. */ > - if (unlikely(*in_num)) { > - vq_err(vq, "Descriptor has out after in: " > - "idx %d\n", i); > - return -EINVAL; > - } > - *out_num += ret; > - } > - } while ((i = next_desc(vq, &desc)) != -1); > - > - /* On success, increment avail index. */ > - vq->last_avail_idx++; > - > - /* Assume notifications from guest are disabled at this point, > - * if they aren't we would need to update avail_event index. */ > - BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY)); > - return head; > -} > -EXPORT_SYMBOL_GPL(vhost_get_vq_desc); > - > static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq) > { > BUG_ON(!vq->ndescs); > @@ -2428,7 +2191,7 @@ static int fetch_indirect_descs(struct vhost_virtqueue *vq, > > /* This function returns a value > 0 if a descriptor was found, or 0 if none were found. > * A negative code is returned on error. */ > -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; > @@ -2441,7 +2204,11 @@ 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 1; > + > if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) { > vq_err(vq, "Failed to access avail idx at %p\n", > &vq->avail->idx); > @@ -2532,6 +2299,41 @@ static int fetch_descs(struct vhost_virtqueue *vq) > return 1; > } > > +/* This function returns a value > 0 if a descriptor was found, or 0 if none were found. > + * A negative code is returned on error. */ > +static int fetch_descs(struct vhost_virtqueue *vq) > +{ > + int ret; > + > + if (unlikely(vq->first_desc >= vq->ndescs)) { > + vq->first_desc = 0; > + vq->ndescs = 0; > + } > + > + if (vq->ndescs) > + return 1; > + > + for (ret = 1; > + ret > 0 && vq->ndescs <= vhost_vq_num_batch_descs(vq); > + ret = fetch_buf(vq)) > + ; > + > + /* On success we expect some descs */ > + BUG_ON(ret > 0 && !vq->ndescs); > + return ret; > +} > + > +/* Reverse the effects of fetch_descs */ > +static void unfetch_descs(struct vhost_virtqueue *vq) > +{ > + int i; > + > + for (i = vq->first_desc; i < vq->ndescs; ++i) > + if (!(vq->descs[i].flags & VRING_DESC_F_NEXT)) > + vq->last_avail_idx -= 1; > + vq->ndescs = 0; > +} > + > /* 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 > @@ -2540,7 +2342,7 @@ static int fetch_descs(struct vhost_virtqueue *vq) > * This function returns the descriptor number found, or vq->num (which is > * never a valid descriptor number) if none was found. A negative code is > * returned on error. */ > -int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq, > +int vhost_get_vq_desc(struct vhost_virtqueue *vq, > struct iovec iov[], unsigned int iov_size, > unsigned int *out_num, unsigned int *in_num, > struct vhost_log *log, unsigned int *log_num) > @@ -2549,7 +2351,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq, > int i; > > if (ret <= 0) > - goto err_fetch; > + goto err; > > /* Now convert to IOV */ > /* When we start there are none of either input nor output. */ > @@ -2557,7 +2359,7 @@ int vhost_get_vq_desc_batch(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; > @@ -2603,24 +2405,26 @@ int vhost_get_vq_desc_batch(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); > -err_fetch: > - vq->ndescs = 0; > + unfetch_descs(vq); > > return ret ? ret : vq->num; > } > -EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch); > +EXPORT_SYMBOL_GPL(vhost_get_vq_desc); > > /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */ > void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n) > { > + unfetch_descs(vq); > vq->last_avail_idx -= n; > } > EXPORT_SYMBOL_GPL(vhost_discard_vq_desc); > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 87089d51490d..fed36af5c444 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; > @@ -189,10 +190,6 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg > bool vhost_vq_access_ok(struct vhost_virtqueue *vq); > bool vhost_log_access_ok(struct vhost_dev *); > > -int vhost_get_vq_desc_batch(struct vhost_virtqueue *, > - struct iovec iov[], unsigned int iov_count, > - unsigned int *out_num, unsigned int *in_num, > - struct vhost_log *log, unsigned int *log_num); > int vhost_get_vq_desc(struct vhost_virtqueue *, > struct iovec iov[], unsigned int iov_count, > unsigned int *out_num, unsigned int *in_num, > @@ -261,6 +258,8 @@ 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; > } > > /**