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Tsirkin" To: Jason Wang Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, eperezma@redhat.com Subject: Re: [PATCH RFC v6 02/11] vhost: use batched get_vq_desc version Message-ID: <20200610070259-mutt-send-email-mst@kernel.org> References: <20200608125238.728563-1-mst@redhat.com> <20200608125238.728563-3-mst@redhat.com> <81904cc5-b662-028d-3b4a-bdfdbd2deb8c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <81904cc5-b662-028d-3b4a-bdfdbd2deb8c@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 10, 2020 at 11:14:49AM +0800, Jason Wang wrote: > > On 2020/6/8 下午8:52, 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 180b7b58c76b..41d6b132c234 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; > > 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; > > +} > > > Is it better to set first_desc to zero here? > > > > + > > /* 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; > > } > > -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; > > > So unfetch_descs() has decreased last_avail_idx. > Can we fix this by letting unfetch_descs() return the number and then we can > do: > > int d = unfetch_descs(vq); > vq->last_avail_idx -= (n > d) ? n - d: 0; > > Thanks That's intentional I think - we need both. Unfetch_descs drops the descriptors in the cache that were *not returned to caller* through get_vq_desc. vhost_discard_vq_desc drops the ones that were returned through get_vq_desc. Did I miss anything? > > > } > > 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; > > } > > /**