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 <m...@redhat.com> Signed-off-by: Eugenio Pérez <epere...@redhat.com> Link: https://lore.kernel.org/r/20200401183118.8334-4-epere...@redhat.com Signed-off-by: Michael S. Tsirkin <m...@redhat.com> --- drivers/vhost/test.c | 2 +- drivers/vhost/vhost.c | 47 ++++++++++++++++++++++++++++++++++++++----- drivers/vhost/vhost.h | 3 +++ 3 files changed, 46 insertions(+), 6 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 33a72edb3ccd..3b0609801381 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; @@ -2179,7 +2189,7 @@ 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; @@ -2192,7 +2202,11 @@ 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); @@ -2283,6 +2297,24 @@ 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 @@ -2308,7 +2340,7 @@ 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; @@ -2354,14 +2386,19 @@ 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 8a7b4191bc48..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; @@ -257,6 +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; } /** -- MST
