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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 F325EC432BE for ; Fri, 27 Aug 2021 14:51:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D594360E97 for ; Fri, 27 Aug 2021 14:51:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245267AbhH0OwH (ORCPT ); Fri, 27 Aug 2021 10:52:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53770 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231327AbhH0OwG (ORCPT ); Fri, 27 Aug 2021 10:52:06 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CC5D0C061757 for ; Fri, 27 Aug 2021 07:51:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fgRwnxGGF057xGl87vsL6kCRqNe7wcNfUYeSw4x56tc=; b=tUg5s6JwGQth/zsyy+aMx5nMrP +lAZJIySGhrCe0H7CM2kWBKnuk6FIHf6r/WjCeqziDWuedqlaDAdsN7hxoSU8UcN422PZpOosugZ8 J00lTUeG67ZQYl7rf76uNjTtnwFqJaOGxmB/Xw4kc9xyEnGHgOzxSqvaXLE8FLZ599ZvhcRDC+97M AvfakezHJEL2qT9ShlZiFjA9Ycv1nH2B6C1bs1EQqbaWqhm1xL5Tu81YDp9VyT+3hBrWjWYO4uKSH HdZU/ay53Y1q+VtjNe1E0+3iZeLhHrozpyie1c0udGm/8pxK+Q5iZ1ovK5u9PJKlSWGt7WBvC9vei 2DUHF8MQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mJd9k-00EfE0-Bn; Fri, 27 Aug 2021 14:48:49 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id EBDE63005AD; Fri, 27 Aug 2021 16:48:30 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C009629A12A4D; Fri, 27 Aug 2021 16:48:30 +0200 (CEST) Date: Fri, 27 Aug 2021 16:48:30 +0200 From: Peter Zijlstra To: Vincent Guittot Cc: Ricardo Neri , Ingo Molnar , Juri Lelli , Srikar Dronamraju , Nicholas Piggin , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Len Brown , Srinivas Pandruvada , Tim Chen , Aubrey Li , "Ravi V. Shankar" , Ricardo Neri , "Rafael J. Wysocki" , Quentin Perret , "Joel Fernandes (Google)" , linuxppc-dev@lists.ozlabs.org, linux-kernel , Aubrey Li , Daniel Bristot de Oliveira Subject: Re: [PATCH v4 6/6] sched/fair: Consider SMT in ASYM_PACKING load balance Message-ID: References: <20210810144145.18776-1-ricardo.neri-calderon@linux.intel.com> <20210810144145.18776-7-ricardo.neri-calderon@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 27, 2021 at 12:13:42PM +0200, Vincent Guittot wrote: > > +/** > > + * asym_smt_can_pull_tasks - Check whether the load balancing CPU can pull tasks > > + * @dst_cpu: Destination CPU of the load balancing > > + * @sds: Load-balancing data with statistics of the local group > > + * @sgs: Load-balancing statistics of the candidate busiest group > > + * @sg: The candidate busiet group > > + * > > + * Check the state of the SMT siblings of both @sds::local and @sg and decide > > + * if @dst_cpu can pull tasks. If @dst_cpu does not have SMT siblings, it can > > + * pull tasks if two or more of the SMT siblings of @sg are busy. If only one > > + * CPU in @sg is busy, pull tasks only if @dst_cpu has higher priority. > > + * > > + * If both @dst_cpu and @sg have SMT siblings, even the number of idle CPUs > > + * between @sds::local and @sg. Thus, pull tasks from @sg if the difference > > + * between the number of busy CPUs is 2 or more. If the difference is of 1, > > + * only pull if @dst_cpu has higher priority. If @sg does not have SMT siblings > > + * only pull tasks if all of the SMT siblings of @dst_cpu are idle and @sg > > + * has lower priority. > > + */ > > +static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds, > > + struct sg_lb_stats *sgs, > > + struct sched_group *sg) > > +{ > > +#ifdef CONFIG_SCHED_SMT > > + bool local_is_smt, sg_is_smt; > > + int sg_busy_cpus; > > + > > + local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY; > > + sg_is_smt = sg->flags & SD_SHARE_CPUCAPACITY; > > + > > + sg_busy_cpus = sgs->group_weight - sgs->idle_cpus; > > + > > + if (!local_is_smt) { > > + /* > > + * If we are here, @dst_cpu is idle and does not have SMT > > + * siblings. Pull tasks if candidate group has two or more > > + * busy CPUs. > > + */ > > + if (sg_is_smt && sg_busy_cpus >= 2) > > + return true; > > + > > + /* > > + * @dst_cpu does not have SMT siblings. @sg may have SMT > > + * siblings and only one is busy. In such case, @dst_cpu > > + * can help if it has higher priority and is idle. > > + */ > > + return !sds->local_stat.group_util && > > sds->local_stat.group_util can't be used to decide if a CPU or group > of CPUs is idle. util_avg is usually not null when a CPU becomes idle > and you can have to wait more than 300ms before it becomes Null > At the opposite, the utilization of a CPU can be null but a task with > null utilization has just woken up on it. > Utilization is used to reflect the average work of the CPU or group of > CPUs but not the current state If you want immediate idle, sgs->nr_running == 0 or sgs->idle_cpus == sgs->group_weight come to mind. > > + sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); > > + } > > + > > + /* @dst_cpu has SMT siblings. */ > > + > > + if (sg_is_smt) { > > + int local_busy_cpus = sds->local->group_weight - > > + sds->local_stat.idle_cpus; > > + int busy_cpus_delta = sg_busy_cpus - local_busy_cpus; > > + > > + /* Local can always help to even the number busy CPUs. */ > > default behavior of the load balance already tries to even the number > of idle CPUs. Right, but I suppose this is because we're trapped here and have to deal with the SMT-SMT case too. Ricardo, can you clarify? > > + if (busy_cpus_delta >= 2) > > + return true; > > + > > + if (busy_cpus_delta == 1) > > + return sched_asym_prefer(dst_cpu, > > + sg->asym_prefer_cpu); > > + > > + return false; > > + } > > + > > + /* > > + * @sg does not have SMT siblings. Ensure that @sds::local does not end > > + * up with more than one busy SMT sibling and only pull tasks if there > > + * are not busy CPUs. As CPUs move in and out of idle state frequently, > > + * also check the group utilization to smoother the decision. > > + */ > > + if (!sds->local_stat.group_util) > > same comment as above about the meaning of group_util == 0 > > > + return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu); > > + > > + return false; > > +#else > > + /* Always return false so that callers deal with non-SMT cases. */ > > + return false; > > +#endif > > +} > > + > > static inline bool > > sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs, > > struct sched_group *group) > > { > > + /* Only do SMT checks if either local or candidate have SMT siblings */ > > + if ((sds->local->flags & SD_SHARE_CPUCAPACITY) || > > + (group->flags & SD_SHARE_CPUCAPACITY)) > > + return asym_smt_can_pull_tasks(env->dst_cpu, sds, sgs, group); > > + > > return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu); > > }