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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49BA2C433EF for ; Mon, 27 Jun 2022 11:00:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233714AbiF0LAD (ORCPT ); Mon, 27 Jun 2022 07:00:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56390 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233897AbiF0LAA (ORCPT ); Mon, 27 Jun 2022 07:00:00 -0400 Received: from mail-wr1-x42d.google.com (mail-wr1-x42d.google.com [IPv6:2a00:1450:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25A566417 for ; Mon, 27 Jun 2022 03:59:59 -0700 (PDT) Received: by mail-wr1-x42d.google.com with SMTP id o16so12502392wra.4 for ; Mon, 27 Jun 2022 03:59:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=mq0qIYAooCDoYXxxt4pMJ0vsx2LS7YQICwC0A7jqELY=; b=s7yPOLeyiVe5npxDJ8DQqZJ5aSxI9PjE8tECTvhzLv+ifKRyIt0svF0+EQ7jPGkxVq gbGdltyr04WDPX8UUC7n/pDdnBMEwV9Q8wIk+5kw2cie9QxRM0Er0l823uyK4hPMA8yw z5aflgm4oPr+aifwDgzCjSpjxUnvBlGp59G6xKPA00CcXwrBABHfCwA/qVEg1xfXvtl0 GIl8rUzBW3np38q3hBC8rA0QMgkiLk5AcNm0Y9s4SQrWfnhA8lZ4vVwbUZ8eZCrru81m F4wT54CIfdWUFlXhZZZm/Jt+7GMbOUDEWKNeaL5d9yFWjqS219j5mKXBcDSzx/9NWa2k mt1w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=mq0qIYAooCDoYXxxt4pMJ0vsx2LS7YQICwC0A7jqELY=; b=PyQapstWWHaTOh4qAhX6OLHNC4Jga10Kg+HIYpaRMq5soSgYbz+W4s7+uqYMYQvE37 lBSRGS9wa1EKaHi/AtVROBWxfOT/I666VmU74uZtqY+yerzBD9g+5YJ+yc0F0TSTCKbO 5Q9i/ziGLhM5r1yMrlkxj3S96+Om3RasDxKBV/bEZk2re85Fe7k9l24X/ox4tQSTvs3h iSA2EG93eIQ1KyE+opJmvCUXl0vqoa4MnD7khPFStOWWNeU9M52dzLWE2tBDjYziTM/G Q1g4zHyGyNf8wN2VWtdIZBhGE0OlVxjkigLS4TrAB7vTgGf6Al6La7w5Z1QwdSPbTju/ 8+tw== X-Gm-Message-State: AJIora997THnr4ijIm5FhJTuib4OPHxoACaeyBfu69VBZA2e93UIOYkc WWRtZjZsmw+CTk3WNtf9fAZjwA== X-Google-Smtp-Source: AGRyM1sV/Dn6dHdP/wHyIjhf0vshgauOZCM1PfbIfYWrG+fi7BeAVVRdoGoNLqmwWyTtu7DFg2qHwQ== X-Received: by 2002:a5d:5a19:0:b0:21b:8eb8:f54b with SMTP id bq25-20020a5d5a19000000b0021b8eb8f54bmr11335986wrb.663.1656327597463; Mon, 27 Jun 2022 03:59:57 -0700 (PDT) Received: from vingu-book ([2a01:e0a:f:6020:1833:5ba3:b4b4:7d8d]) by smtp.gmail.com with ESMTPSA id d9-20020a05600c3ac900b003a03be22f9fsm13387618wms.18.2022.06.27.03.59.56 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Mon, 27 Jun 2022 03:59:56 -0700 (PDT) Date: Mon, 27 Jun 2022 12:59:54 +0200 From: Vincent Guittot To: Zhang Qiao Cc: David Chen , "linux-kernel@vger.kernel.org" , Ingo Molnar Subject: Re: Perf regression from scheduler load_balance rework in 5.5? Message-ID: <20220627105954.GA7670@vingu-book> References: <409fc8d0-119a-3358-0fc5-99a786a9564a@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <409fc8d0-119a-3358-0fc5-99a786a9564a@huawei.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Le vendredi 24 juin 2022 à 21:16:05 (+0800), Zhang Qiao a écrit : > > Hi, > 在 2022/6/24 16:22, Vincent Guittot 写道: > > On Thu, 23 Jun 2022 at 21:50, David Chen wrote: > >> > >> Hi, > >> > >> I'm working on upgrading our kernel from 4.14 to 5.10 > >> However, I'm seeing performance regression when doing rand read from windows client through smbd > >> with a well cached file. > >> > >> One thing I noticed is that on the new kernel, the smbd thread doing socket I/O tends to stay on > >> the same cpu core as the net_rx softirq, where as in the old kernel it tends to be moved around > >> more randomly. And when they are on the same cpu, it tends to saturate the cpu more and causes > >> performance to drop. > >> > >> For example, here's the duration (ns) the thread spend on each cpu I captured using bpftrace > >> On 4.14: > >> @cputime[7]: 20741458382 > >> @cputime[0]: 25219285005 > >> @cputime[6]: 30892418441 > >> @cputime[5]: 31032404613 > >> @cputime[3]: 33511324691 > >> @cputime[1]: 35564174562 > >> @cputime[4]: 39313421965 > >> @cputime[2]: 55779811909 (net_rx cpu) > >> > >> On 5.10: > >> @cputime[3]: 2150554823 > >> @cputime[5]: 3294276626 > >> @cputime[7]: 4277890448 > >> @cputime[4]: 5094586003 > >> @cputime[1]: 6058168291 > >> @cputime[0]: 14688093441 > >> @cputime[6]: 17578229533 > >> @cputime[2]: 223473400411 (net_rx cpu) > >> > >> I also tried setting the cpu affinity of the smbd thread away from the net_rx cpu and indeed that > >> seems to bring the perf on par with old kernel. > > I observed the same problem for the past two weeks. > > >> > >> I noticed that there's scheduler load_balance rework in 5.5, so I did the test on 5.4 and 5.5 and > >> it did show the behavior changed between 5.4 and 5.5. > > > > Have you tested v5.18 ? several improvements happened since v5.5 > > > >> > >> Anyone know how to work around this? > > > > Have you enabled IRQ_TIME_ACCOUNTING ? > > > CONFIG_IRQ_TIME_ACCOUNTING=y. > > > > > When the time spent under interrupt becomes significant, scheduler > > migrate task on another cpu > > > My board has two cpus, and i used iperf3 to test upload bandwidth，then I saw the same situation， > the iperf3 thread run on the same cpu as the NET_RX softirq. > > After debug in find_busiest_group(), i noticed when the cpu(env->idle is CPU_IDLE or CPU_NEWLY_IDLE) try to pull task, > the busiest->group_type == group_fully_busy, busiest->sum_h_nr_running == 1, local->group_type==group_has_spare, > and the loadbalance will failed at find_busiest_group(), as follows: > > find_busiest_group(): > ... > if (busiest->group_type != group_overloaded) { > .... > if (busiest->sum_h_nr_running == 1) > goto out_balanced; ----> loadbalance will returned at here. Yes, you're right, we filter such case. Could you try the patch below ? I use the misfit task state to detect cpu with reduced capacity and migrate_load to check if it worth migration the task on the dst cpu. diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6775a117f3c1..013dcd97472b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8757,11 +8757,19 @@ static inline void update_sg_lb_stats(struct lb_env *env, if (local_group) continue; - /* Check for a misfit task on the cpu */ - if (env->sd->flags & SD_ASYM_CPUCAPACITY && - sgs->group_misfit_task_load < rq->misfit_task_load) { - sgs->group_misfit_task_load = rq->misfit_task_load; - *sg_status |= SG_OVERLOAD; + if (env->sd->flags & SD_ASYM_CPUCAPACITY) { + /* Check for a misfit task on the cpu */ + if (sgs->group_misfit_task_load < rq->misfit_task_load) { + sgs->group_misfit_task_load = rq->misfit_task_load; + *sg_status |= SG_OVERLOAD; + } + } else if ((env->idle != CPU_NOT_IDLE) && + (group->group_weight == 1) && + (rq->cfs.h_nr_running == 1) && + check_cpu_capacity(rq, env->sd) && + (sgs->group_misfit_task_load < cpu_load(rq))) { + /* Check for a task running on a CPU with reduced capacity */ + sgs->group_misfit_task_load = cpu_load(rq); } } @@ -8814,7 +8822,8 @@ static bool update_sd_pick_busiest(struct lb_env *env, * CPUs in the group should either be possible to resolve * internally or be covered by avg_load imbalance (eventually). */ - if (sgs->group_type == group_misfit_task && + if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && + (sgs->group_type == group_misfit_task) && (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || sds->local_stat.group_type != group_has_spare)) return false; @@ -9360,9 +9369,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s busiest = &sds->busiest_stat; if (busiest->group_type == group_misfit_task) { - /* Set imbalance to allow misfit tasks to be balanced. */ - env->migration_type = migrate_misfit; - env->imbalance = 1; + if (env->sd->flags & SD_ASYM_CPUCAPACITY) { + /* Set imbalance to allow misfit tasks to be balanced. */ + env->migration_type = migrate_misfit; + env->imbalance = 1; + } else { + /* Set group overloaded as one cpu has reduced capacity */ + env->migration_type = migrate_load; + env->imbalance = busiest->group_misfit_task_load; + } return; } > .... > > > Thanks, > Qiao > > > > Vincent>> > >> Thanks, > >> David > > . > >