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,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 22AB5C433ED for ; Fri, 2 Apr 2021 13:04:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC49C610D1 for ; Fri, 2 Apr 2021 13:04:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235540AbhDBNEv (ORCPT ); Fri, 2 Apr 2021 09:04:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234628AbhDBNEt (ORCPT ); Fri, 2 Apr 2021 09:04:49 -0400 Received: from mail-lj1-x22e.google.com (mail-lj1-x22e.google.com [IPv6:2a00:1450:4864:20::22e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0AD7BC0613E6 for ; Fri, 2 Apr 2021 06:04:48 -0700 (PDT) Received: by mail-lj1-x22e.google.com with SMTP id u9so5521124ljd.11 for ; Fri, 02 Apr 2021 06:04:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=LIFPdn2HHsJa4KRcR9pDTGoB9KgM4sDHiRfQccA6W5U=; b=AsvJSEILIC/U78Qs6F3cN7SEwON/POywBtYUSwyo1xftp6jW00S0Y04HS+l6q+79s2 xuO4vIQ9fuAG4TIdJFM7vVnwihw8V8hB+tw/aI7in8ARJwXwNt34tKZv1OgZECJk/m42 gMdYKqyAAA6Ross+ozOU076p8oiAPtdQxe4odJ4hkchZAJ/lOPkktrcPExQ6fcvIq6QX K480/d2W1S8yx+uQmq0zEZ06W89lfySt75TZXOAq/w5B6dICOS56i0vTOllmWM3lbVW5 KaX2nqolP/ukLgzYchmdQpzgL1o9VACEAMYcUjubfD4WbeGlOQHMa/C8rngdEQPyAk/j FOIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=LIFPdn2HHsJa4KRcR9pDTGoB9KgM4sDHiRfQccA6W5U=; b=sOyXUXkfH7KXvF4BO+FZOf1ZXFlX8cwChIIqbnnnFlbo2O3ohZRqLN9mlg2twoSHxi ko0mODKaLHZPA2DqJ4fY3aAJZv9M0sV89X7sqhX2OKz+vat+fksQ0CMY1EV/3MNYxNaZ Y5tZVsm3yy6n095pEgmVbea07NBv4sUFuuU+d2n/C4lC4lgnRV6Idz6djly1s4Qn8g00 sWplVA/8VlYIfq82Su8gjScCd/VDqunzfqQoO+NSrRRxlJWw+POICwNNyvexg0706T9n TP2zGytQcBuVtfap42yDQCNyg4WN7RrGttrTnXVpTSArunwnk1VhsHHrNNRDYOQs+MYf +qFg== X-Gm-Message-State: AOAM532NsGtcutSvg138nVKh+CyGLOFE7sm4uvkCnYUeFEXigliJS20H Nd1HeWm7bCx33BliEQ91zf98bdRa9qk2NEFqRV3VtMfdWZAxag== X-Google-Smtp-Source: ABdhPJxHCa4PCEFHZt0fRpsYAQJwJjxmWIAEgjMWDJNUvxQdy88JPvzFb8PNk6kNLHULx7jwwZm8LFSOlyq06gbhS8A= X-Received: by 2002:a05:651c:282:: with SMTP id b2mr8003028ljo.176.1617368685440; Fri, 02 Apr 2021 06:04:45 -0700 (PDT) MIME-Version: 1.0 References: <20210401193006.3392788-1-valentin.schneider@arm.com> <20210401193006.3392788-4-valentin.schneider@arm.com> In-Reply-To: <20210401193006.3392788-4-valentin.schneider@arm.com> From: Vincent Guittot Date: Fri, 2 Apr 2021 15:04:34 +0200 Message-ID: Subject: Re: [PATCH v4 3/3] sched/fair: Introduce a CPU capacity comparison helper To: Valentin Schneider Cc: linux-kernel , Qais Yousef , Lingutla Chandrasekhar , Peter Zijlstra , Ingo Molnar , Dietmar Eggemann , Morten Rasmussen , Quentin Perret , Pavan Kondeti , Rik van Riel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Apr 2021 at 21:30, Valentin Schneider wrote: > > During load-balance, groups classified as group_misfit_task are filtered > out if they do not pass > > group_smaller_max_cpu_capacity(, ); > > which itself employs fits_capacity() to compare the sgc->max_capacity of > both groups. > > Due to the underlying margin, fits_capacity(X, 1024) will return false for > any X > 819. Tough luck, the capacity_orig's on e.g. the Pixel 4 are > {261, 871, 1024}. If a CPU-bound task ends up on one of those "medium" > CPUs, misfit migration will never intentionally upmigrate it to a CPU of > higher capacity due to the aforementioned margin. > > One may argue the 20% margin of fits_capacity() is excessive in the advent > of counter-enhanced load tracking (APERF/MPERF, AMUs), but one point here > is that fits_capacity() is meant to compare a utilization value to a > capacity value, whereas here it is being used to compare two capacity > values. As CPU capacity and task utilization have different dynamics, a > sensible approach here would be to add a new helper dedicated to comparing > CPU capacities. > > While at it, replace group_smaller_{min, max}_cpu_capacity() with > comparisons of the source group's min/max capacity and the destination > CPU's capacity. > > Reviewed-by: Qais Yousef > Tested-by: Lingutla Chandrasekhar > Signed-off-by: Valentin Schneider Reviewed-by: Vincent Guittot > --- > kernel/sched/fair.c | 33 ++++++++++----------------------- > 1 file changed, 10 insertions(+), 23 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index d8077f82a380..c9c5c2697998 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -113,6 +113,13 @@ int __weak arch_asym_cpu_priority(int cpu) > */ > #define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024) > > +/* > + * The margin used when comparing CPU capacities. > + * is 'cap1' noticeably greater than 'cap2' > + * > + * (default: ~5%) > + */ > +#define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078) > #endif > > #ifdef CONFIG_CFS_BANDWIDTH > @@ -8364,26 +8371,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs) > return false; > } > > -/* > - * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller > - * per-CPU capacity than sched_group ref. > - */ > -static inline bool > -group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > -{ > - return fits_capacity(sg->sgc->min_capacity, ref->sgc->min_capacity); > -} > - > -/* > - * group_smaller_max_cpu_capacity: Returns true if sched_group sg has smaller > - * per-CPU capacity_orig than sched_group ref. > - */ > -static inline bool > -group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > -{ > - return fits_capacity(sg->sgc->max_capacity, ref->sgc->max_capacity); > -} > - > static inline enum > group_type group_classify(unsigned int imbalance_pct, > struct sched_group *group, > @@ -8539,7 +8526,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, > * internally or be covered by avg_load imbalance (eventually). > */ > if (sgs->group_type == group_misfit_task && > - (!group_smaller_max_cpu_capacity(sg, sds->local) || > + (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) || > sds->local_stat.group_type != group_has_spare)) > return false; > > @@ -8623,7 +8610,7 @@ static bool update_sd_pick_busiest(struct lb_env *env, > */ > if ((env->sd->flags & SD_ASYM_CPUCAPACITY) && > (sgs->group_type <= group_fully_busy) && > - (group_smaller_min_cpu_capacity(sds->local, sg))) > + (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu)))) > return false; > > return true; > @@ -9423,7 +9410,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, > * average load. > */ > if (env->sd->flags & SD_ASYM_CPUCAPACITY && > - capacity_of(env->dst_cpu) < capacity && > + !capacity_greater(capacity_of(env->dst_cpu), capacity) && > nr_running == 1) > continue; > > -- > 2.25.1 >