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 9AD54C4332F for ; Fri, 16 Dec 2022 23:17:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229510AbiLPXRR (ORCPT ); Fri, 16 Dec 2022 18:17:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230205AbiLPXQr (ORCPT ); Fri, 16 Dec 2022 18:16:47 -0500 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B47C663D3B; Fri, 16 Dec 2022 15:16:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1671232576; x=1702768576; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=4TwMHbHcz5c58OOhZoR8gaykEMG0kQlgrEFXlEMBq9o=; b=E1Sz8i17m6dAu8GSgOCUtpO+5u961J6AI7yfYJiQW7dF9QfxKzLvQAIn 59EvmvbTnbqMgLPu3nuNGJFKzLvZAfmMM3RdTHvfipZfXUxcrMtEjgpCu mOC5Nh5f/sBXZAoZu1ThwNYWcVGcPjejpGcC/twb+sQjddE8J/YAsgh/R tihOTLAyy4EqKYaRMkfCAUwHlaP/3DiUM6/F3FqF7HFy1ecVXh7aCka2Y WpNEXrw2gttQZy2gDVLlwM6BNmRehXWxTHtQoIKg4DsuiB6GjB3W62PyN WuSaTAN0jfO4L4DR6IkPe9IpB9osw43X8gLrlyrMNjDGF1JRevxf8dSsa Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10563"; a="302497732" X-IronPort-AV: E=Sophos;i="5.96,251,1665471600"; d="scan'208";a="302497732" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Dec 2022 15:16:10 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10563"; a="643419690" X-IronPort-AV: E=Sophos;i="5.96,251,1665471600"; d="scan'208";a="643419690" Received: from ranerica-svr.sc.intel.com ([172.25.110.23]) by orsmga007.jf.intel.com with ESMTP; 16 Dec 2022 15:15:47 -0800 Date: Fri, 16 Dec 2022 15:24:06 -0800 From: Ricardo Neri To: Ionela Voinescu Cc: "Peter Zijlstra (Intel)" , Juri Lelli , Vincent Guittot , Ricardo Neri , "Ravi V. Shankar" , Ben Segall , Daniel Bristot de Oliveira , Dietmar Eggemann , Len Brown , Mel Gorman , "Rafael J. Wysocki" , Srinivas Pandruvada , Steven Rostedt , Tim Chen , Valentin Schneider , x86@kernel.org, "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Tim C . Chen" Subject: Re: [PATCH v2 09/22] sched/fair: Use IPC class score to select a busiest runqueue Message-ID: <20221216232406.GA23530@ranerica-svr.sc.intel.com> References: <20221128132100.30253-1-ricardo.neri-calderon@linux.intel.com> <20221128132100.30253-10-ricardo.neri-calderon@linux.intel.com> <20221214003243.GC30234@ranerica-svr.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 14, 2022 at 11:16:39PM +0000, Ionela Voinescu wrote: > Hi Ricardo, > > On Tuesday 13 Dec 2022 at 16:32:43 (-0800), Ricardo Neri wrote: > [..] > > > > /** > > > > @@ -10419,8 +10442,8 @@ static struct rq *find_busiest_queue(struct lb_env *env, > > > > { > > > > struct rq *busiest = NULL, *rq; > > > > unsigned long busiest_util = 0, busiest_load = 0, busiest_capacity = 1; > > > > + int i, busiest_ipcc_delta = INT_MIN; > > > > unsigned int busiest_nr = 0; > > > > - int i; > > > > > > > > for_each_cpu_and(i, sched_group_span(group), env->cpus) { > > > > unsigned long capacity, load, util; > > > > @@ -10526,8 +10549,37 @@ static struct rq *find_busiest_queue(struct lb_env *env, > > > > > > > > case migrate_task: > > > > if (busiest_nr < nr_running) { > > > > + struct task_struct *curr; > > > > + > > > > busiest_nr = nr_running; > > > > busiest = rq; > > > > + > > > > + /* > > > > + * Remember the IPC score delta of busiest::curr. > > > > + * We may need it to break a tie with other queues > > > > + * with equal nr_running. > > > > + */ > > > > + curr = rcu_dereference(busiest->curr); > > > > + busiest_ipcc_delta = ipcc_score_delta(curr, > > > > + env->dst_cpu); > > > > + /* > > > > + * If rq and busiest have the same number of running > > > > + * tasks, pick rq if doing so would give rq::curr a > > > > + * bigger IPC boost on dst_cpu. > > > > + */ > > > > + } else if (sched_ipcc_enabled() && > > > > + busiest_nr == nr_running) { > > > > + struct task_struct *curr; > > > > + int delta; > > > > + > > > > + curr = rcu_dereference(rq->curr); > > > > + delta = ipcc_score_delta(curr, env->dst_cpu); > > > > + > > > > + if (busiest_ipcc_delta < delta) { > > > > + busiest_ipcc_delta = delta; > > > > + busiest_nr = nr_running; > > > > + busiest = rq; > > > > + } > > > > } > > > > break; > > > > > > > > > > While in the commit message you describe this as breaking a tie for > > > asym_packing, > > > > Are you referring to the overall series or this specific patch? I checked > > commit message and I do not see references to asym_packing. > > Sorry, my bad, I was thinking about the cover letter, not the commit > message. It's under "+++ Balancing load using classes of tasks. Theory > of operation". > > > > > > the code here does not only affect asym_packing. If > > > another architecture would have sched_ipcc_enabled() it would use this > > > as generic policy, and that might not be desired. > > > > Indeed, the patchset implements support to use IPCC classes for asym_packing, > > but it is not limited to it. > > > > So is your current intention to support IPC classes only for asym_packing > for now? My intention is to introduce IPC classes in general and make it available to other policies or architectures. I use asym_packing as use case. > What would be the impact on you if you were to limit the > functionality in this patch to asym_packing only? There would not be any adverse impact. > > > It is true that I don't check here for asym_packing, but it should not be a > > problem, IMO. I compare two runqueues with equal nr_running, either runqueue > > is a good choice. This tie breaker is an overall improvement, no? > > > > It could be, but equally there could be other better policies as well - > other ways to consider IPC class information to break the tie. > > If other architectures start having sched_ipcc_enabled() they would > automatically use the policy you've decided on here. If other policies > are better for those architectures this generic policy would be difficult > to modify to ensure there are no regressions for all other architectures > that use it, or it would be difficult to work around it. > > For this and for future support of IPC classes I am just wondering if we > can better design how we enable different architectures to have different > policies. I see your point. I agree that other architectures may want to implement policies differently. I'll add an extra check for env->sd & SD_ASYM_PACKING. Thanks and BR, Ricardo