From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA1CCC433E2 for ; Wed, 22 Jul 2020 08:04:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A471120792 for ; Wed, 22 Jul 2020 08:04:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="C70VoXmx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726807AbgGVIEd (ORCPT ); Wed, 22 Jul 2020 04:04:33 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:30685 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726573AbgGVIEc (ORCPT ); Wed, 22 Jul 2020 04:04:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595405070; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nb0bmuOR5AabZ9/kmNkKSWj6VAfofR2sm0D19qrFIWw=; b=C70VoXmxHlIsl3Qsq/VfzjEOAaihX7JgUfiZpINWL5mI5qTm7TdgwilBGudBnG2jCy9QiJ 56VmLbYEEITBVYQ/ygjYvhSqZHR4DElkGdHSTQO3IGdf75VGS5VFjR53Mc26iHdIOu5tl0 tWTgrlsCBh0zNNhOlIyKE6/Ju+M/07Y= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-493-rurFKqdUPPCDlNJHLIdkmw-1; Wed, 22 Jul 2020 04:04:27 -0400 X-MC-Unique: rurFKqdUPPCDlNJHLIdkmw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 822EA18C63C1; Wed, 22 Jul 2020 08:04:24 +0000 (UTC) Received: from T590 (ovpn-13-96.pek2.redhat.com [10.72.13.96]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 42410610AF; Wed, 22 Jul 2020 08:04:13 +0000 (UTC) Date: Wed, 22 Jul 2020 16:04:09 +0800 From: Ming Lei To: Kashyap Desai Cc: John Garry , axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com, don.brace@microsemi.com, Sumit Saxena , bvanassche@acm.org, hare@suse.com, hch@lst.de, Shivasharan Srikanteshwara , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, esc.storagedev@microsemi.com, chenxiang66@hisilicon.com, "PDL,MEGARAIDLINUX" Subject: Re: [PATCH RFC v7 10/12] megaraid_sas: switch fusion adapters to MQ Message-ID: <20200722080409.GB912316@T590> References: <61299951-97dc-b2be-c66c-024dfbd3a1cb@huawei.com> <13d6b63e-3aa8-68fa-29ab-a4c202024280@huawei.com> <34a832717fef4702b143ea21aa12b79e@mail.gmail.com> <1dcf2bb9-142c-7bb8-9207-5a1b792eb3f9@huawei.com> <20200721011323.GA833377@T590> <20200722041201.GA912316@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Wed, Jul 22, 2020 at 11:00:45AM +0530, Kashyap Desai wrote: > > On Tue, Jul 21, 2020 at 12:23:39PM +0530, Kashyap Desai wrote: > > > > > > > > > > > > Perf top (shared host tag. IOPS = 230K) > > > > > > > > > > > > 13.98% [kernel] [k] sbitmap_any_bit_set > > > > > > 6.43% [kernel] [k] blk_mq_run_hw_queue > > > > > > > > > > blk_mq_run_hw_queue function take more CPU which is called from " > > > > > scsi_end_request" > > > > > > > > The problem could be that nr_hw_queues is increased a lot so that > > > > sample > > > on > > > > blk_mq_run_hw_queue() can be observed now. > > > > > > Yes. That is correct. > > > > > > > > > > > > It looks like " blk_mq_hctx_has_pending" handles only elevator > > > > > (scheduler) case. If queue has ioscheduler=none, we can skip. I > > > > > case of scheduler=none, IO will be pushed to hardware queue and it > > > > > by pass > > > > software queue. > > > > > Based on above understanding, I added below patch and I can see > > > > > performance scale back to expectation. > > > > > > > > > > Ming mentioned that - we cannot remove blk_mq_run_hw_queues() > > from > > > > > IO completion path otherwise we may see IO hang. So I have just > > > > > modified completion path assuming it is only required for IO > scheduler > > case. > > > > > https://www.spinics.net/lists/linux-block/msg55049.html > > > > > > > > > > Please review and let me know if this is good or we have to > > > > > address with proper fix. > > > > > > > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c index > > > > > 1be7ac5a4040..b6a5b41b7fc2 100644 > > > > > --- a/block/blk-mq.c > > > > > +++ b/block/blk-mq.c > > > > > @@ -1559,6 +1559,9 @@ void blk_mq_run_hw_queues(struct > > > > request_queue > > > > > *q, bool async) > > > > > struct blk_mq_hw_ctx *hctx; > > > > > int i; > > > > > > > > > > + if (!q->elevator) > > > > > + return; > > > > > + > > > > > > > > This way shouldn't be correct, blk_mq_run_hw_queues() is still > > > > needed > > > for > > > > none because request may not be dispatched successfully by direct > issue. > > > > > > When block layer attempt posting request to h/w queue directly (for > > > ioscheduler=none) and if it fails, it is calling > > > blk_mq_request_bypass_insert(). > > > blk_mq_request_bypass_insert function will start the h/w queue from > > > submission context. Do we still have an issue if we skip running hw > > > queue from completion ? > > > > The thing is that we can't guarantee that direct issue or adding request > into > > hctx->dispatch is always done for MQ/none, for example, request still > > can be added to sw queue from blk_mq_flush_plug_list() when mq plug is > > applied. > > I see even blk_mq_sched_insert_requests() from blk_mq_flush_plug_list make > sure it run the h/w queue. If all the submission path which deals with s/w > queue make sure they run h/w queue, can't we remove blk_mq_run_hw_queues() > from scsi_end_request ? No, one purpose of blk_mq_run_hw_queues() is for rerun queue in case that dispatch budget is running out of in submission path, and sdev->device_busy is shared by all hw queues on this scsi device. I posted one patch for avoiding it in scsi_end_request() before, looks it never lands upstream: https://lore.kernel.org/linux-block/20191118100640.3673-1-ming.lei@redhat.com/ Thanks, Ming