Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964787AbaF1S2o (ORCPT ); Sat, 28 Jun 2014 14:28:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:53782 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755658AbaF1Ru6 (ORCPT ); Sat, 28 Jun 2014 13:50:58 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Rusty Russell , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, Ming Lei , Jens Axboe Subject: [PATCH 3.15 002/139] block: virtio_blk: dont hold spin lock during world switch Date: Sat, 28 Jun 2014 10:46:03 -0700 Message-Id: <20140628174605.469557168@linuxfoundation.org> X-Mailer: git-send-email 2.0.1 In-Reply-To: <20140628174605.352098823@linuxfoundation.org> References: <20140628174605.352098823@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ming Lei commit e8edca6f7f92234202d6dd163c118ef495244d7c upstream. Firstly, it isn't necessary to hold lock of vblk->vq_lock when notifying hypervisor about queued I/O. Secondly, virtqueue_notify() will cause world switch and it may take long time on some hypervisors(such as, qemu-arm), so it isn't good to hold the lock and block other vCPUs. On arm64 quad core VM(qemu-kvm), the patch can increase I/O performance a lot with VIRTIO_RING_F_EVENT_IDX enabled: - without the patch: 14K IOPS - with the patch: 34K IOPS fio script: [global] direct=1 bsrange=4k-4k timeout=10 numjobs=4 ioengine=libaio iodepth=64 filename=/dev/vdc group_reporting=1 [f1] rw=randread Cc: Rusty Russell Cc: "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org Signed-off-by: Ming Lei Acked-by: Rusty Russell Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- drivers/block/virtio_blk.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -159,6 +159,7 @@ static int virtio_queue_rq(struct blk_mq unsigned int num; const bool last = (req->cmd_flags & REQ_END) != 0; int err; + bool notify = false; BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); @@ -211,10 +212,12 @@ static int virtio_queue_rq(struct blk_mq return BLK_MQ_RQ_QUEUE_ERROR; } - if (last) - virtqueue_kick(vblk->vq); - + if (last && virtqueue_kick_prepare(vblk->vq)) + notify = true; spin_unlock_irqrestore(&vblk->vq_lock, flags); + + if (notify) + virtqueue_notify(vblk->vq); return BLK_MQ_RQ_QUEUE_OK; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/