[PATCH v3 3/8] vhost: use batched version by default

Eugenio Pérez
2020-03-31T19:28:56Z

From: "Michael S. Tsirkin" <mst@redhat.com>

As testing shows no performance change, switch to that now.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
drivers/vhost/vhost.c | 251 +-----------------------------------------
drivers/vhost/vhost.h | 4 -
2 files changed, 2 insertions(+), 253 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 38e65a36465b..56c5253056ee 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2113,253 +2113,6 @@ 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);
@@ -2570,7 +2323,7 @@ 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)
@@ -2645,7 +2398,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *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)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a6fc11797a8a..1dbb5e44fba4 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -203,10 +203,6 @@ 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,
--
2.18.1