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=-16.0 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 C1FF2C433E0 for ; Tue, 12 Jan 2021 02:17:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8847422510 for ; Tue, 12 Jan 2021 02:17:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728245AbhALCRF (ORCPT ); Mon, 11 Jan 2021 21:17:05 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41438 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726852AbhALCRE (ORCPT ); Mon, 11 Jan 2021 21:17:04 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610417737; 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=jgKPBduqRysl0E0nB/9cv+OQX+mWuuzaD8tbbZgBaK4=; b=g3o1yhTDFhYtGFV/fYz/zlhIp67UnwRdSWNgVQmCFrttpgDQG417tzzVAxrd1uBznxUte4 h+x9kdM+p9DsHDlbQdsDBAUeROozaETzOoWsgOxiuKA3gNcNDAHjSewuoqEKozvwCUujed 5wh1zN2OE2BTeSUCIqss60h3TNkpzd8= 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-530-MglOTa3xMQKGk1L8EzNzdg-1; Mon, 11 Jan 2021 21:15:36 -0500 X-MC-Unique: MglOTa3xMQKGk1L8EzNzdg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 247BD9CC03; Tue, 12 Jan 2021 02:15:35 +0000 (UTC) Received: from T590 (ovpn-13-57.pek2.redhat.com [10.72.13.57]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71D7810013BD; Tue, 12 Jan 2021 02:15:30 +0000 (UTC) Date: Tue, 12 Jan 2021 10:15:26 +0800 From: Ming Lei To: Jan Kara Cc: Jens Axboe , linux-block@vger.kernel.org Subject: Re: [PATCH 2/2] blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues Message-ID: <20210112021526.GC60605@T590> References: <20210111164717.21937-1-jack@suse.cz> <20210111164717.21937-3-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111164717.21937-3-jack@suse.cz> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Jan 11, 2021 at 05:47:17PM +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 | 66 ++++++++++++++++++++++++++++++++++++---- > block/kyber-iosched.c | 1 + > include/linux/elevator.h | 2 ++ > 3 files changed, 63 insertions(+), 6 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 57f3482b2c26..580601787f7a 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1646,6 +1646,42 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) > } > EXPORT_SYMBOL(blk_mq_run_hw_queue); > > +/* > + * Is the request queue handled by an IO scheduler that does not respect > + * hardware queues when dispatching? > + */ > +static bool blk_mq_has_sqsched(struct request_queue *q) > +{ > + struct elevator_queue *e = q->elevator; > + > + if (e && e->type->ops.dispatch_request && > + !(e->type->elevator_features & ELEVATOR_F_MQ_AWARE)) > + return true; > + return false; > +} > + > +/* > + * Return prefered queue to dispatch from (if any) for non-mq aware IO > + * scheduler. > + */ > +static struct blk_mq_hw_ctx *blk_mq_get_sq_hctx(struct request_queue *q) > +{ > + struct blk_mq_hw_ctx *hctx; > + > + /* > + * If the IO scheduler does not respect hardware queues when > + * dispatching, we 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. > + */ > + 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. > @@ -1653,14 +1689,23 @@ EXPORT_SYMBOL(blk_mq_run_hw_queue); > */ > void blk_mq_run_hw_queues(struct request_queue *q, bool async) > { > - struct blk_mq_hw_ctx *hctx; > + struct blk_mq_hw_ctx *hctx, *sq_hctx; > int i; > > + sq_hctx = NULL; > + if (blk_mq_has_sqsched(q)) > + sq_hctx = blk_mq_get_sq_hctx(q); > queue_for_each_hw_ctx(q, hctx, i) { > if (blk_mq_hctx_stopped(hctx)) > continue; > - > - blk_mq_run_hw_queue(hctx, async); > + /* > + * Dispatch from this hctx either if there's no hctx preferred > + * by IO scheduler or if it has requests that bypass the > + * scheduler. > + */ > + if (!sq_hctx || sq_hctx == hctx || > + !list_empty_careful(&hctx->dispatch)) > + blk_mq_run_hw_queue(hctx, async); > } > } > EXPORT_SYMBOL(blk_mq_run_hw_queues); > @@ -1672,14 +1717,23 @@ EXPORT_SYMBOL(blk_mq_run_hw_queues); > */ > void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs) > { > - struct blk_mq_hw_ctx *hctx; > + struct blk_mq_hw_ctx *hctx, *sq_hctx; > int i; > > + sq_hctx = NULL; > + if (blk_mq_has_sqsched(q)) > + sq_hctx = blk_mq_get_sq_hctx(q); > queue_for_each_hw_ctx(q, hctx, i) { > if (blk_mq_hctx_stopped(hctx)) > continue; > - > - blk_mq_delay_run_hw_queue(hctx, msecs); > + /* > + * Dispatch from this hctx either if there's no hctx preferred > + * by IO scheduler or if it has requests that bypass the > + * scheduler. > + */ > + if (!sq_hctx || sq_hctx == hctx || > + !list_empty_careful(&hctx->dispatch)) > + blk_mq_delay_run_hw_queue(hctx, msecs); > } > } > EXPORT_SYMBOL(blk_mq_delay_run_hw_queues); > diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c > index dc89199bc8c6..c25c41d0d061 100644 > --- a/block/kyber-iosched.c > +++ b/block/kyber-iosched.c > @@ -1029,6 +1029,7 @@ static struct elevator_type kyber_sched = { > #endif > .elevator_attrs = kyber_sched_attrs, > .elevator_name = "kyber", > + .elevator_features = ELEVATOR_F_MQ_AWARE, > .elevator_owner = THIS_MODULE, > }; > > diff --git a/include/linux/elevator.h b/include/linux/elevator.h > index bacc40a0bdf3..1fe8e105b83b 100644 > --- a/include/linux/elevator.h > +++ b/include/linux/elevator.h > @@ -172,6 +172,8 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t); > > /* Supports zoned block devices sequential write constraint */ > #define ELEVATOR_F_ZBD_SEQ_WRITE (1U << 0) > +/* Supports scheduling on multiple hardware queues */ > +#define ELEVATOR_F_MQ_AWARE (1U << 1) > > #endif /* CONFIG_BLOCK */ > #endif > -- > 2.26.2 > Reviewed-by: Ming Lei -- Ming