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[79.176.10.77]) by smtp.gmail.com with ESMTPSA id y58sm5129799qta.1.2019.10.11.06.46.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Oct 2019 06:46:08 -0700 (PDT) Date: Fri, 11 Oct 2019 09:46:04 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: [PATCH RFC v1 2/2] vhost: batching fetches Message-ID: <20191011134358.16912-3-mst@redhat.com> References: <20191011134358.16912-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191011134358.16912-1-mst@redhat.com> X-Mailer: git-send-email 2.22.0.678.g13338e74b8 X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 --- drivers/vhost/test.c | 2 +- drivers/vhost/vhost.c | 50 ++++++++++++++++++++++++++++++++++++------- drivers/vhost/vhost.h | 4 +++- 3 files changed, 46 insertions(+), 10 deletions(-) diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c index 39a018a7af2d..e3a8e9db22cd 100644 --- a/drivers/vhost/test.c +++ b/drivers/vhost/test.c @@ -128,7 +128,7 @@ 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); f->private_data = n; diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 36661d6cb51f..aa383e847865 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -302,6 +302,7 @@ 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; @@ -390,6 +391,7 @@ 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; + vq->batch_descs = dev->iov_limit - UIO_MAXIOV; vq->descs = kmalloc_array(vq->max_descs, sizeof(*vq->descs), GFP_KERNEL); @@ -2366,6 +2368,8 @@ static void pop_split_desc(struct vhost_virtqueue *vq) --vq->ndescs; } +#define VHOST_DESC_FLAGS (VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE | \ + VRING_DESC_F_NEXT) static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc, u16 id) { struct vhost_desc *h; @@ -2375,7 +2379,7 @@ static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc, h = &vq->descs[vq->ndescs++]; h->addr = vhost64_to_cpu(vq, desc->addr); h->len = vhost32_to_cpu(vq, desc->len); - h->flags = vhost16_to_cpu(vq, desc->flags); + h->flags = vhost16_to_cpu(vq, desc->flags) & VHOST_DESC_FLAGS; h->id = id; return 0; @@ -2450,7 +2454,7 @@ 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) { struct vring_desc desc; unsigned int i, head, found = 0; @@ -2462,7 +2466,11 @@ 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); @@ -2541,6 +2549,24 @@ 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 <= vq->batch_descs) + 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 @@ -2562,6 +2588,8 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq, if (ret) return ret; + /* Note: indirect descriptors are not batched */ + /* TODO: batch up to a limit */ last = peek_split_desc(vq); id = last->id; @@ -2584,12 +2612,12 @@ 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; - if (desc->flags & ~(VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE)) { + if (desc->flags & ~VHOST_DESC_FLAGS) { vq_err(vq, "Unexpected flags: 0x%x at descriptor id 0x%x\n", desc->flags, desc->id); ret = -EINVAL; @@ -2628,15 +2656,21 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq, } *out_num += ret; } + + ret = desc->id; + + if (!(desc->flags & VRING_DESC_F_NEXT)) + break; } - ret = id; - 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 (!(desc->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 1724f61b6c2d..8b88e0c903da 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -100,7 +100,9 @@ struct vhost_virtqueue { struct vhost_desc *descs; int ndescs; + int first_desc; int max_descs; + int batch_descs; const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS]; struct file *kick; @@ -245,7 +247,7 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev, int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled); #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) -- MST