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vhost: add unlikely annotations to error path
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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>
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Michael S. Tsirkin committed Jul 1, 2010
1 parent d5675bd commit 7b3384f
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Showing 2 changed files with 29 additions and 28 deletions.
4 changes: 2 additions & 2 deletions drivers/vhost/net.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -137,7 +137,7 @@ static void handle_tx(struct vhost_net *net)
&out, &in,
NULL, NULL);
/* On error, stop handling until the next kick. */
if (head < 0)
if (unlikely(head < 0))
break;
/* Nothing new? Wait for eventfd to tell us they refilled. */
if (head == vq->num) {
Expand Down Expand Up @@ -234,7 +234,7 @@ static void handle_rx(struct vhost_net *net)
&out, &in,
vq_log, &log);
/* On error, stop handling until the next kick. */
if (head < 0)
if (unlikely(head < 0))
break;
/* OK, now we need to know about added descriptors. */
if (head == vq->num) {
Expand Down
53 changes: 27 additions & 26 deletions drivers/vhost/vhost.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
Expand Down Expand Up @@ -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,
Expand All @@ -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;
}
Expand All @@ -813,35 +813,35 @@ 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;
}

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;
}

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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand All @@ -909,15 +909,16 @@ 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]);
return -EFAULT;
}

/* 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;
Expand All @@ -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;
Expand All @@ -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;
Expand All @@ -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;
Expand All @@ -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;
Expand Down

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