From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org
Subject: [PATCH] vhost: replace % with & on data path
Date: Mon, 30 Nov 2015 10:34:07 +0200 [thread overview]
Message-ID: <1448872427-11623-1-git-send-email-mst@redhat.com> (raw)
We know vring num is a power of 2, so use &
to mask the high bits.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 080422f..85f0f0a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1366,10 +1366,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
/* 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(__get_user(ring_head,
- &vq->avail->ring[last_avail_idx % vq->num]))) {
+ &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
vq_err(vq, "Failed to read head: idx %d address %p\n",
last_avail_idx,
&vq->avail->ring[last_avail_idx % vq->num]);
@@ -1489,7 +1491,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
u16 old, new;
int start;
- start = vq->last_used_idx % vq->num;
+ start = vq->last_used_idx & (vq->num - 1);
used = vq->used->ring + start;
if (count == 1) {
if (__put_user(heads[0].id, &used->id)) {
@@ -1531,7 +1533,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
{
int start, n, r;
- start = vq->last_used_idx % vq->num;
+ start = vq->last_used_idx & (vq->num - 1);
n = vq->num - start;
if (n < count) {
r = __vhost_add_used_n(vq, heads, n);
--
MST
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: [PATCH] vhost: replace % with & on data path
Date: Mon, 30 Nov 2015 10:34:07 +0200 [thread overview]
Message-ID: <1448872427-11623-1-git-send-email-mst@redhat.com> (raw)
We know vring num is a power of 2, so use &
to mask the high bits.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 080422f..85f0f0a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1366,10 +1366,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
/* 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(__get_user(ring_head,
- &vq->avail->ring[last_avail_idx % vq->num]))) {
+ &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
vq_err(vq, "Failed to read head: idx %d address %p\n",
last_avail_idx,
&vq->avail->ring[last_avail_idx % vq->num]);
@@ -1489,7 +1491,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
u16 old, new;
int start;
- start = vq->last_used_idx % vq->num;
+ start = vq->last_used_idx & (vq->num - 1);
used = vq->used->ring + start;
if (count == 1) {
if (__put_user(heads[0].id, &used->id)) {
@@ -1531,7 +1533,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
{
int start, n, r;
- start = vq->last_used_idx % vq->num;
+ start = vq->last_used_idx & (vq->num - 1);
n = vq->num - start;
if (n < count) {
r = __vhost_add_used_n(vq, heads, n);
--
MST
next reply other threads:[~2015-11-30 8:34 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-30 8:34 Michael S. Tsirkin [this message]
2015-11-30 8:34 ` [PATCH] vhost: replace % with & on data path Michael S. Tsirkin
2015-11-30 8:42 ` Joe Perches
2015-11-30 8:42 ` Joe Perches
2015-11-30 9:21 ` Michael S. Tsirkin
2015-11-30 9:21 ` Michael S. Tsirkin
2015-11-30 9:00 ` kbuild test robot
2015-11-30 9:00 ` kbuild test robot
2015-11-30 9:05 ` kbuild test robot
2015-11-30 9:05 ` kbuild test robot
2015-11-30 9:11 ` Michael S. Tsirkin
2015-11-30 9:11 ` Michael S. Tsirkin
2015-11-30 9:18 ` kbuild test robot
2015-11-30 9:18 ` kbuild test robot
2015-11-30 16:13 ` David Miller
2015-11-30 16:13 ` David Miller
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