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[23.128.96.18]) by mx.google.com with ESMTP id nv14si28859861pjb.143.2021.10.10.06.22.56; Sun, 10 Oct 2021 06:23:08 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=YF4qb1AC; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232259AbhJJMWK (ORCPT + 99 others); Sun, 10 Oct 2021 08:22:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231892AbhJJMWJ (ORCPT ); Sun, 10 Oct 2021 08:22:09 -0400 Received: from mail-ed1-x52f.google.com (mail-ed1-x52f.google.com [IPv6:2a00:1450:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 445D4C061570 for ; Sun, 10 Oct 2021 05:20:11 -0700 (PDT) Received: by mail-ed1-x52f.google.com with SMTP id g8so55905463edt.7 for ; Sun, 10 Oct 2021 05:20:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=W6gACDj/nR9KQ5fYNRZFJLVHSwItch9IypvQdL4rOY0=; b=YF4qb1ACARvxAYxTiMkd76XzDZqXnYwRf06zPmoD3XEjlNpzUgQIX1uaP9xKYVRN9F I2gINWIRyu/fhlyqMq/LAzOIoiRqAKLdz3BuUC2IbAVpYhhLtRlG43uNMosnuSVM+ech WUOY5f0hu8VAMNvsEP6krYwGEoD9rP8rvQ4cgZa7dhHgy5eIqmsb6MJd0C2mDEaPGXyZ fBCqCyd3czbboaK6pTSalR2hYCSPUNpe4HY7ll9jk7Eioi1UVhLDgbdp7ucq4ON7kjHi GLMhZZlRJghjK8dNUy/og90nRRXFSrWK/2pzamXr9pasTQANjuFO3uQg95E4TnlnVGiZ iNEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=W6gACDj/nR9KQ5fYNRZFJLVHSwItch9IypvQdL4rOY0=; b=eQK/+ENWPlGxEfcgvqEeOsWWkixtnVQUo/Msu/fJjNMLEPm2BSxyu7LtHlaNCcJnFy qDOTJvM6l29vo+nvpKNA45fm1UuFyBmwNqLSwqZYC8xdXPCchJbvE5QUI/zygMQfMumB KhGt/deJ/pdBbhWbgluLuH2meLuyYRkPOaKpI9x8ameYtOZQHcAlwZ1t0DYBuj4dV7BU 5tFrVNdgyvG08PQST8hervQLM7Ux/gMyEGvsYvhONUqpeG4Uq99u7U2AmEWtxCSvhLYA WwyUO8kJ6hT4VqoWrXRl+a9Ivsqx3jpqktggRxkfjbhAiecnyoRbwcUFOwqGlsy90T+O 7DKg== X-Gm-Message-State: AOAM532oHe9CCjjqc3fuyB1+V0LViBL1I5g9KLWApqT/Z1YcHyoHI77k dC7ArivwDrVhSgUBODfKAIy9IEy9X8thXzQok5g= X-Received: by 2002:a17:907:767a:: with SMTP id kk26mr18006411ejc.134.1633868409786; Sun, 10 Oct 2021 05:20:09 -0700 (PDT) MIME-Version: 1.0 References: <20211009180941.20458-1-tao.zhou@linux.dev> <20211009225057.GB174703@worktop.programming.kicks-ass.net> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Mon, 11 Oct 2021 01:19:57 +1300 Message-ID: Subject: Re: [PATCH] sched/fair: Check idle_cpu in select_idle_core/cpu() To: Tao Zhou Cc: Peter Zijlstra , LKML , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 10, 2021 at 10:45 PM Tao Zhou wrote: > > Hi Peter, > > On Sun, Oct 10, 2021 at 12:50:57AM +0200, Peter Zijlstra wrote: > > On Sun, Oct 10, 2021 at 02:09:41AM +0800, Tao Zhou wrote: > > > In select_idle_core(), the idle core returned may have no cpu > > > allowed. I think the idle core returned for the task is the one > > > that can be allowed to run. I insist on this semantics. > > > > > > In select_idle_cpu(), if select_idle_core() can not find the > > > idle core, one reason is that the core is not allowed for the > > > task, but the core itself is idle from the point of > > > sds->has_idle_cores. I insist on this semantics. > > > > > > No others, just two additional check. > > > --- > > > kernel/sched/fair.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index f6a05d9b5443..a44aca5095d3 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -6213,7 +6213,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu > > > *idle_cpu = cpu; > > > } > > > > > > - if (idle) > > > + if (idle && *idle_cpu != -1) > > > return core; > > > > In that case, core would be nr_cpu_ids (==nr_cpumask_bits), and then the caller checks: > > > > (unsigned)i < nr_cpumask_bits > > Thank you for reply. > > > If (1)there is no idle core or (2)the idle core has no allowed cpu, we return -1. > Originally, just (1) has happened, we return -1. The (2) is what I want to add. I don't understand (2). before doing for_each_cpu_wrap(cpu, cpus, target + 1) { if (has_idle_core) { i = select_idle_core(p, cpu, cpus, &idle_cpu); if ((unsigned int)i < nr_cpumask_bits) return i; } else { if (!--nr) return -1; idle_cpu = __select_idle_cpu(cpu, p); if ((unsigned int)idle_cpu < nr_cpumask_bits) break; } } to select idle core, we have already done: cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); so we are only scanning allowed cpus. > > If we find idle core and has allowed cpu in the core, is it better to return > @*idle_cpu. > > if (idle && *idle_cpu != -1) > return *idle_cpu; > > This @*idle_cpu is the allowed cpu in the idle core. We do not promise anything > about the @core(target) is the allowed cpu until we hit in select_task_rq() --> > select_fallback_rq(). And the select_fallback_rq() will return a different cpu > than the @core or @*idle_cpu. > > > > cpumask_andnot(cpus, cpus, cpu_smt_mask(core)); > > > @@ -6324,7 +6324,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > > > } > > > } > > > > > > - if (has_idle_core) > > > + if (has_idle_core && *idle_cpu != -1) > > > set_idle_cores(target, false); > > > > And this one I'm completely failing, why shouldn't we mark the core as > > non-idle when there is a single idle CPU found? That's just worng. > > When @has_idle_core is true, it implies for all cpu in the core the case > (1) or case (2) has happened. The (1) can be mark as non-idle. I conclude > to contradiction myself last time. The (2) is also seemed to be non-idle. > > > But, I think I am totally wrong because the sds->has_idle_cores is related > to the cpu not task. So, the affinity should not affect the decision of > sds->has_idle_cores. > > > > Thanks, > Tao Thanks barry