From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Hajnoczi Subject: [PATCH v2 2/2] virtio_blk: unlock vblk->lock during kick Date: Wed, 7 Sep 2011 14:51:41 +0100 Message-ID: <1315403501-12457-3-git-send-email-stefanha@linux.vnet.ibm.com> References: <1315403501-12457-1-git-send-email-stefanha@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1315403501-12457-1-git-send-email-stefanha@linux.vnet.ibm.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: virtualization@lists.linux-foundation.org Cc: Khoa Huynh , Christoph Hellwig , Stefan Hajnoczi , "Michael S. Tsirkin" List-Id: virtualization@lists.linuxfoundation.org Holding the vblk->lock across kick causes poor scalability in SMP guests. If one CPU is doing virtqueue kick and another CPU touches the vblk->lock it will have to spin until virtqueue kick completes. This typically results in high system CPU utilization in SMP guests that are running multithreaded I/O-bound workloads. Signed-off-by: Stefan Hajnoczi --- drivers/block/virtio_blk.c | 10 ++++++++-- 1 files changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 079c088..c2bf0a9 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -193,8 +193,14 @@ static void do_virtblk_request(struct request_queue *q) issued++; } - if (issued) - virtqueue_kick(vblk->vq); + if (!issued) + return; + + if (virtqueue_kick_prepare(vblk->vq)) { + spin_unlock(&vblk->lock); + virtqueue_kick_notify(vblk->vq); + spin_lock(&vblk->lock); + } } /* return id (s/n) string for *disk to *id_str -- 1.7.5.4