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[109.64.41.91]) by smtp.gmail.com with ESMTPSA id a3sm3462243wmb.7.2020.06.02.06.06.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jun 2020 06:06:02 -0700 (PDT) Date: Tue, 2 Jun 2020 09:06:01 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Eugenio =?utf-8?b?UMOpcmV6?= , Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: [PATCH RFC 03/13] vhost: batching fetches Message-ID: <20200602130543.578420-4-mst@redhat.com> References: <20200602130543.578420-1-mst@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200602130543.578420-1-mst@redhat.com> X-Mailer: git-send-email 2.24.1.751.gd10ce2899c X-Mutt-Fcc: =sent Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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; +} + 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__); \ 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; } /**