Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752559AbbEDUfq (ORCPT ); Mon, 4 May 2015 16:35:46 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:5523 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751985AbbEDUfl (ORCPT ); Mon, 4 May 2015 16:35:41 -0400 Message-ID: <5547D815.7060100@fb.com> Date: Mon, 4 May 2015 14:35:33 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Shaohua Li CC: Jeff Moyer , , , Subject: Re: [PATCH 4/5] blk-mq: do limited block plug for multiple queue case References: <20150504194037.GA3300441@devbig257.prn2.facebook.com> <5547CCA9.2000003@fb.com> <20150504203356.GA3541245@devbig257.prn2.facebook.com> In-Reply-To: <20150504203356.GA3541245@devbig257.prn2.facebook.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.13.68,1.0.33,0.0.0000 definitions=2015-05-04_04:2015-05-04,2015-05-04,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1757 Lines: 41 On 05/04/2015 02:33 PM, Shaohua Li wrote: > On Mon, May 04, 2015 at 01:46:49PM -0600, Jens Axboe wrote: >> On 05/04/2015 01:40 PM, Shaohua Li wrote: >>> On Fri, May 01, 2015 at 04:16:04PM -0400, Jeff Moyer wrote: >>>> Shaohua Li writes: >>>> >>>>> plug is still helpful for workload with IO merge, but it can be harmful >>>>> otherwise especially with multiple hardware queues, as there is >>>>> (supposed) no lock contention in this case and plug can introduce >>>>> latency. For multiple queues, we do limited plug, eg plug only if there >>>>> is request merge. If a request doesn't have merge with following >>>>> request, the requet will be dispatched immediately. >>>>> >>>>> This also fixes a bug. If we directly issue a request and it fails, we >>>>> use blk_mq_merge_queue_io(). But we already assigned bio to a request in >>>>> blk_mq_bio_to_request. blk_mq_merge_queue_io shouldn't run >>>>> blk_mq_bio_to_request again. >>>> >>>> Good catch. Might've been better to split that out first for easy >>>> backport to stable kernels, but I won't hold you to that. >>> >>> It's not a severe bug, but I don't mind. Jens, please let me know if I >>> should split the patch into 2 patches. >> >> I don't care that much for this particular case. But since one/more >> of the others need respin anyway, might be prudent to split it up in >> any case. > > ok, done. I'll repost the patch 4/5. Please let me know if I should > repost 1-3. That's fine, I'll grab 1-3 as-is. Thanks! -- Jens Axboe -- 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/