vhost: add unlikely annotations to error path

patch 'break out of polling loop on error' caused
a minor performance regression on my machine: recover
that performance by adding a bunch of unlikely annotations
in the error handling.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 27 insertions, 26 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 5ccd384ec0be..0b99783083f6 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -736,12 +736,12 @@ static int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
         mem = rcu_dereference(dev->memory);
         while ((u64)len > s) {
                 u64 size;
-                if (ret >= iov_size) {
+                if (unlikely(ret >= iov_size)) {
                         ret = -ENOBUFS;
                         break;
                 }
                 reg = find_region(mem, addr, len);
-                if (!reg) {
+                if (unlikely(!reg)) {
                         ret = -EFAULT;
                         break;
                 }
@@ -780,18 +780,18 @@ static unsigned next_desc(struct vring_desc *desc)
         return next;
 }
 
-static unsigned get_indirect(struct vhost_dev *dev, 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)
+static int get_indirect(struct vhost_dev *dev, 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;
         int ret;
 
         /* Sanity check */
-        if (indirect->len % sizeof desc) {
+        if (unlikely(indirect->len % sizeof desc)) {
                 vq_err(vq, "Invalid length in indirect descriptor: "
                        "len 0x%llx not multiple of 0x%zx\n",
                        (unsigned long long)indirect->len,
@@ -801,7 +801,7 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
         ret = translate_desc(dev, indirect->addr, indirect->len, vq->indirect,
                              ARRAY_SIZE(vq->indirect));
-        if (ret < 0) {
+        if (unlikely(ret < 0)) {
                 vq_err(vq, "Translation failure %d in indirect.\n", ret);
                 return ret;
         }
@@ -813,7 +813,7 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
         count = indirect->len / sizeof desc;
         /* Buffers are chained via a 16 bit next field, so
          * we can have at most 2^16 of these. */
-        if (count > USHRT_MAX + 1) {
+        if (unlikely(count > USHRT_MAX + 1)) {
                 vq_err(vq, "Indirect buffer length too big: %d\n",
                        indirect->len);
                 return -E2BIG;
@@ -821,19 +821,19 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
         do {
                 unsigned iov_count = *in_num + *out_num;
-                if (++found > count) {
+                if (unlikely(++found > count)) {
                         vq_err(vq, "Loop detected: last one at %u "
                                "indirect size %u\n",
                                i, count);
                         return -EINVAL;
                 }
-                if (memcpy_fromiovec((unsigned char *)&desc, vq->indirect,
-                                     sizeof desc)) {
+                if (unlikely(memcpy_fromiovec((unsigned char *)&desc, vq->indirect,
+                                              sizeof desc))) {
                         vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
                                i, (size_t)indirect->addr + i * sizeof desc);
                         return -EINVAL;
                 }
-                if (desc.flags & VRING_DESC_F_INDIRECT) {
+                if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
                         vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
                                i, (size_t)indirect->addr + i * sizeof desc);
                         return -EINVAL;
@@ -841,7 +841,7 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
                 ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
                                      iov_size - iov_count);
-                if (ret < 0) {
+                if (unlikely(ret < 0)) {
                         vq_err(vq, "Translation failure %d indirect idx %d\n",
                                ret, i);
                         return ret;
@@ -857,7 +857,7 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                 } else {
                         /* If it's an output descriptor, they're all supposed
                          * to come before any input descriptors. */
-                        if (*in_num) {
+                        if (unlikely(*in_num)) {
                                 vq_err(vq, "Indirect descriptor "
                                        "has out after in: idx %d\n", i);
                                 return -EINVAL;
@@ -888,13 +888,13 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
         /* Check it isn't doing very strange things with descriptor numbers. */
         last_avail_idx = vq->last_avail_idx;
-        if (get_user(vq->avail_idx, &vq->avail->idx)) {
+        if (unlikely(get_user(vq->avail_idx, &vq->avail->idx))) {
                 vq_err(vq, "Failed to access avail idx at %p\n",
                        &vq->avail->idx);
                 return -EFAULT;
         }
 
-        if ((u16)(vq->avail_idx - last_avail_idx) > vq->num) {
+        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;
@@ -909,7 +909,8 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
         /* Grab the next descriptor number they're advertising, and increment
          * the index we've seen. */
-        if (get_user(head, &vq->avail->ring[last_avail_idx % vq->num])) {
+        if (unlikely(get_user(head,
+                              &vq->avail->ring[last_avail_idx % vq->num]))) {
                 vq_err(vq, "Failed to read head: idx %d address %p\n",
                        last_avail_idx,
                        &vq->avail->ring[last_avail_idx % vq->num]);
@@ -917,7 +918,7 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
         }
 
         /* If their number is silly, that's an error. */
-        if (head >= vq->num) {
+        if (unlikely(head >= vq->num)) {
                 vq_err(vq, "Guest says index %u > %u is available",
                        head, vq->num);
                 return -EINVAL;
@@ -931,19 +932,19 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
         i = head;
         do {
                 unsigned iov_count = *in_num + *out_num;
-                if (i >= vq->num) {
+                if (unlikely(i >= vq->num)) {
                         vq_err(vq, "Desc index is %u > %u, head = %u",
                                i, vq->num, head);
                         return -EINVAL;
                 }
-                if (++found > vq->num) {
+                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 = copy_from_user(&desc, vq->desc + i, sizeof desc);
-                if (ret) {
+                if (unlikely(ret)) {
                         vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
                                i, vq->desc + i);
                         return -EFAULT;
@@ -952,7 +953,7 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                         ret = get_indirect(dev, vq, iov, iov_size,
                                            out_num, in_num,
                                            log, log_num, &desc);
-                        if (ret < 0) {
+                        if (unlikely(ret < 0)) {
                                 vq_err(vq, "Failure detected "
                                        "in indirect descriptor at idx %d\n", i);
                                 return ret;
@@ -962,7 +963,7 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
                 ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
                                      iov_size - iov_count);
-                if (ret < 0) {
+                if (unlikely(ret < 0)) {
                         vq_err(vq, "Translation failure %d descriptor idx %d\n",
                                ret, i);
                         return ret;
@@ -979,7 +980,7 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                 } else {
                         /* If it's an output descriptor, they're all supposed
                          * to come before any input descriptors. */
-                        if (*in_num) {
+                        if (unlikely(*in_num)) {
                                 vq_err(vq, "Descriptor has out after in: "
                                        "idx %d\n", i);
                                 return -EINVAL;