From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PULL 2/2] vhost: replace rcu with mutex Date: Tue, 3 Jun 2014 00:30:18 +0300 Message-ID: <1401744482-17764-3-git-send-email-mst@redhat.com> References: <1401744482-17764-1-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1401744482-17764-1-git-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org, David Miller , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org 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)" Signed-off-by: Michael S. Tsirkin --- 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