From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751977AbaKJDQf (ORCPT ); Sun, 9 Nov 2014 22:16:35 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:51272 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751745AbaKJDQd (ORCPT ); Sun, 9 Nov 2014 22:16:33 -0500 Message-ID: <54602E0E.6060409@kernel.dk> Date: Sun, 09 Nov 2014 20:16:30 -0700 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Paolo Bonzini , linux-kernel@vger.kernel.org CC: Thomas Gleixner , Clark Williams Subject: Re: [PATCH 0/2] blk-mq: switch from preempt_disable/enable to get/put_cpu References: <1415397840-18041-1-git-send-email-pbonzini@redhat.com> In-Reply-To: <1415397840-18041-1-git-send-email-pbonzini@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014-11-07 15:03, Paolo Bonzini wrote: > blk-mq is using preempt_disable/enable in order to ensure that the > queue runners are placed on the right CPU. This does not work with > the RT patches, because __blk_mq_run_hw_queue takes a non-raw > spinlock with the preemption-disabled region. If there is contention > on the lock, this violates the rules for preemption-disabled regions. > > While this could be fixed easily within the RT patches just by doing > migrate_disable/enable (note: this was not tested :)), we can do > better. The first patch concentrates the preempt_disable/enable in > a single place in blk_mq_run_hw_queue, and also avoids useless calls > when the caller wants to start __blk_mq_run_hw_queue asynchronously. > (There is already a call to __blk_mq_run_hw_queue that does not disable > preemption in blk-flush.c; not coincidentially, it passes async=true). > > Once this is done, it is trivial to use get/put_cpu instead of > preempt_disable/smp_processor_id/preempt_enable, which is what the > second patch does. The RT patches then can change this to use > get_cpu_light. > > With these changes (and the additional switch to get_cpu_light), > virtio-blk can be used again with RT kernels. These both look good. I'll double check and run through some testing, then apply for 3.19 if it all passes. -- Jens Axboe