[PULL 2/2] vhost: replace rcu with mutex

Michael S. Tsirkin
2014-06-02T21:30:18Z

All memory accesses are done under some VQ mutex.
So lock/unlock all VQs is a faster equivalent of synchronize_rcu()
for memory access changes.
Some guests cause a lot of these changes, so it's helpful
to make them faster.

Reported-by: "Gonglei (Arei)" <arei.gonglei@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 78987e4..1c05e60 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -593,6 +593,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
{
struct vhost_memory mem, *newmem, *oldmem;
unsigned long size = offsetof(struct vhost_memory, regions);
+ int i;

if (copy_from_user(&mem, m, size))
return -EFAULT;
@@ -619,7 +620,14 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
oldmem = rcu_dereference_protected(d->memory,
lockdep_is_held(&d->mutex));
rcu_assign_pointer(d->memory, newmem);
- synchronize_rcu();
+
+ /* All memory accesses are done under some VQ mutex.
+ * So below is a faster equivalent of synchronize_rcu()
+ */
+ for (i = 0; i < d->nvqs; ++i) {
+ mutex_lock(&d->vqs[i]->mutex);
+ mutex_unlock(&d->vqs[i]->mutex);
+ }
kfree(oldmem);
return 0;
}
--
MST