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vhost: replace rcu with mutex 

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>
This commit is contained in:
Michael S. Tsirkin 2014-05-28 17:07:02 +03:00
parent 23cc5a991c
commit 98f9ca0a3f
1 changed files with 9 additions and 1 deletions
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10
drivers/vhost/vhost.c
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@ -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;
}