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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 C4ED1C4361B for ; Sat, 19 Dec 2020 03:16:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BFA42343F for ; Sat, 19 Dec 2020 03:16:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726287AbgLSDQN (ORCPT ); Fri, 18 Dec 2020 22:16:13 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57257 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726254AbgLSDQM (ORCPT ); Fri, 18 Dec 2020 22:16:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608347685; 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=JiuSNAQOlu0rR3XYkESK4Mm7vyPIgraiPXrH+3DIUlg=; b=BjGi0EUTmCi1tSAxUbNfnyasMhOUx8fF58dhURSe7VCpNZXEC5FqNb1rXlJWzFwqdA7bsR qe2ejL4z5e0miZCShBcpH8RrijLLzYPAkvlCNkCd4cfCygoPwpyay2MSDNFDp7pSgJdGs0 2Z2Vrzyvi8ejCoad6if1Q6hp28PRuGY= 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-437-Ol-jnUHfPiOF9e0uzmVNaQ-1; Fri, 18 Dec 2020 22:14:41 -0500 X-MC-Unique: Ol-jnUHfPiOF9e0uzmVNaQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E3FC8107ACE3; Sat, 19 Dec 2020 03:14:39 +0000 (UTC) Received: from T590 (ovpn-12-79.pek2.redhat.com [10.72.12.79]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3937D2BCC0; Sat, 19 Dec 2020 03:14:31 +0000 (UTC) Date: Sat, 19 Dec 2020 11:14:27 +0800 From: Ming Lei To: Jan Kara Cc: Jens Axboe , linux-block@vger.kernel.org, hare@suse.de, Kashyap Desai Subject: Re: [PATCH 2/2] blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues Message-ID: <20201219031427.GA2711539@T590> References: <20201218214412.1543-1-jack@suse.cz> <20201218214412.1543-3-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201218214412.1543-3-jack@suse.cz> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Dec 18, 2020 at 10:44:12PM +0100, Jan Kara wrote: > Currently when non-mq aware IO scheduler (BFQ, mq-deadline) is used for > a queue with multiple HW queues, the performance it rather bad. The > problem is that these IO schedulers use queue-wide locking and their > dispatch function does not respect the hctx it is passed in and returns > any request it finds appropriate. Thus locality of request access is > broken and dispatch from multiple CPUs just contends on IO scheduler > locks. For these IO schedulers there's little point in dispatching from > multiple CPUs. Instead dispatch always only from a single CPU to limit > contention. > > Below is a comparison of dbench runs on XFS filesystem where the storage > is a raid card with 64 HW queues and to it attached a single rotating > disk. BFQ is used as IO scheduler: > > clients MQ SQ MQ-Patched > Amean 1 39.12 (0.00%) 43.29 * -10.67%* 36.09 * 7.74%* > Amean 2 128.58 (0.00%) 101.30 * 21.22%* 96.14 * 25.23%* > Amean 4 577.42 (0.00%) 494.47 * 14.37%* 508.49 * 11.94%* > Amean 8 610.95 (0.00%) 363.86 * 40.44%* 362.12 * 40.73%* > Amean 16 391.78 (0.00%) 261.49 * 33.25%* 282.94 * 27.78%* > Amean 32 324.64 (0.00%) 267.71 * 17.54%* 233.00 * 28.23%* > Amean 64 295.04 (0.00%) 253.02 * 14.24%* 242.37 * 17.85%* > Amean 512 10281.61 (0.00%) 10211.16 * 0.69%* 10447.53 * -1.61%* > > Numbers are times so lower is better. MQ is stock 5.10-rc6 kernel. SQ is > the same kernel with megaraid_sas.host_tagset_enable=0 so that the card > advertises just a single HW queue. MQ-Patched is a kernel with this > patch applied. > > You can see multiple hardware queues heavily hurt performance in > combination with BFQ. The patch restores the performance. > > Signed-off-by: Jan Kara > --- > block/blk-mq.c | 37 +++++++++++++++++++++++++++++++++++++ > block/kyber-iosched.c | 1 + > include/linux/elevator.h | 2 ++ > 3 files changed, 40 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 57d0461f2be5..6d80054c231b 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1663,6 +1663,31 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) > } > EXPORT_SYMBOL(blk_mq_run_hw_queue); > > +static struct blk_mq_hw_ctx *blk_mq_sq_iosched_hctx(struct request_queue *q) > +{ > + struct elevator_queue *e = q->elevator; > + struct blk_mq_hw_ctx *hctx; > + > + /* > + * The queue has multiple hardware queues but uses IO scheduler that > + * does not respect hardware queues when dispatching? This is not a > + * great setup but it can be sensible when we have a single rotational > + * disk behind a raid card. Just don't bother with multiple HW queues > + * and dispatch from hctx for the current CPU since running multiple > + * queues just causes lock contention inside the scheduler and > + * pointless cache bouncing because the hctx is not respected by the IO > + * scheduler's dispatch function anyway. > + */ > + if (q->nr_hw_queues > 1 && e && e->type->ops.dispatch_request && > + !(e->type->elevator_features & ELEVATOR_F_MQ_AWARE)) { > + hctx = blk_mq_map_queue_type(q, HCTX_TYPE_DEFAULT, > + raw_smp_processor_id()); > + if (!blk_mq_hctx_stopped(hctx)) > + return hctx; > + } > + return NULL; > +} > + > /** > * blk_mq_run_hw_queues - Run all hardware queues in a request queue. > * @q: Pointer to the request queue to run. > @@ -1673,6 +1698,12 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) > struct blk_mq_hw_ctx *hctx; > int i; > > + hctx = blk_mq_sq_iosched_hctx(q); > + if (hctx) { > + blk_mq_run_hw_queue(hctx, async); > + return; > + } > + This approach looks reasonable, just wondering which code path is wrt. blk_mq_run_hw_queues() improvement by this patch. Since ed5dd6a67d5e ("scsi: core: Only re-run queue in scsi_end_request() if device queue is busy") is merged, blk_mq_run_hw_queues() is only called from scsi_end_request() when the scsi device is busy for megaraid. Another one is bfq_schedule_dispatch(), in which blk_mq_run_hw_queues() is still be called, if that is the reason, maybe it is easier to optimize bfq_schedule_dispatch() by avoiding to call blk_mq_run_hw_queues(). thanks, Ming