From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754426AbaE3DTS (ORCPT ); Thu, 29 May 2014 23:19:18 -0400 Received: from mail-pb0-f47.google.com ([209.85.160.47]:38925 "EHLO mail-pb0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751919AbaE3DTR (ORCPT ); Thu, 29 May 2014 23:19:17 -0400 Message-ID: <5387F8B2.1070509@kernel.dk> Date: Thu, 29 May 2014 21:19:14 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Ming Lei , linux-kernel@vger.kernel.org CC: Rusty Russell , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org Subject: Re: [PATCH] block: virtio_blk: don't hold spin lock during world switch References: <1401418169-3361-1-git-send-email-ming.lei@canonical.com> In-Reply-To: <1401418169-3361-1-git-send-email-ming.lei@canonical.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014-05-29 20:49, Ming Lei wrote: > 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 Patch looks good to me. I don't see a hit on my qemu-kvm testing, but it definitely makes sense and I can see it hurting in other places. -- Jens Axboe