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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 E061FC3F2CE for ; Wed, 4 Mar 2020 18:22:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4D1324684 for ; Wed, 4 Mar 2020 18:22:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="NY2qlbYB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730137AbgCDSWP (ORCPT ); Wed, 4 Mar 2020 13:22:15 -0500 Received: from merlin.infradead.org ([205.233.59.134]:48828 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729675AbgCDSWO (ORCPT ); Wed, 4 Mar 2020 13:22:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=hKyWk7Lq9ur1Op8sObVzpsl0Nt0c5ZcDaJMgGzKn8JE=; b=NY2qlbYBsu9O8vYaS7tyE5l9MV AmD64y52Ym5b+53nu8nhjjIy86DdgdzHv6M9XPy1Bt8m1eTKWH26Sa2J/6i0vUl56tBwnidlxdItv hm0VLOonJMI+2O7PSHkchFj27+lL/fwtdiH3pTNTiyCM+Eju56n7fANmWpnTPp02ivGzw+zvZcGgs Qa4iJO2RjOyDxcLNQMIjcKk8ZdLwAkXVgWMaqwxRJMRtm5qCGJ4XDDBCi0vJuNHoEIANp3RdDJa4A 2vpc/fIpflsJyq2WIkJSnfHqtMUjPam47XOnMJnkjtQpi9CVGUsqfteXwJ1PWVF0Gk8CFu6HrONx3 uOByesWA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j9YeM-0002BO-IQ; Wed, 04 Mar 2020 18:21:43 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id E36C8303DA3; Wed, 4 Mar 2020 19:19:40 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9213E23CE6B20; Wed, 4 Mar 2020 19:21:39 +0100 (CET) Date: Wed, 4 Mar 2020 19:21:39 +0100 From: Peter Zijlstra To: Josh Don Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Li Zefan , Tejun Heo , Johannes Weiner , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Paul Turner Subject: Re: [PATCH] sched/cpuset: distribute tasks within affinity masks Message-ID: <20200304182139.GO2596@hirez.programming.kicks-ass.net> References: <20200228010134.42866-1-joshdon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200228010134.42866-1-joshdon@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 27, 2020 at 05:01:34PM -0800, Josh Don wrote: > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 04278493bf15..a2aab6a8a794 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1587,6 +1587,8 @@ extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_ > #ifdef CONFIG_SMP > extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask); > extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask); > +extern int set_cpus_allowed_ptr_distribute(struct task_struct *p, > + const struct cpumask *new_mask); Why? Changelog doesn't seem to give a reason for adding another interface. > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1a9983da4408..2336d6d66016 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1612,6 +1612,32 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) > set_next_task(rq, p); > } > > +static DEFINE_PER_CPU(int, distribute_cpu_mask_prev); > + > +/* > + * Returns an arbitrary cpu within *srcp1 & srcp2 > + * > + * Iterated calls using the same srcp1 and srcp2, passing the previous cpu each > + * time, will be distributed within their intersection. > + */ > +static int distribute_to_new_cpumask(const struct cpumask *src1p, > + const struct cpumask *src2p) > +{ > + int next, prev; > + > + /* NOTE: our first selection will skip 0. */ > + prev = __this_cpu_read(distribute_cpu_mask_prev); > + > + next = cpumask_next_and(prev, src1p, src2p); > + if (next >= nr_cpu_ids) > + next = cpumask_first_and(src1p, src2p); > + > + if (next < nr_cpu_ids) > + __this_cpu_write(distribute_cpu_mask_prev, next); > + > + return next; > +} That's a valid implementation of cpumask_any_and(), it just has a really weird name. > /* > * Change a given task's CPU affinity. Migrate the thread to a > * proper CPU and schedule it away if the CPU it's executing on > @@ -1621,11 +1647,11 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) > * task must not exit() & deallocate itself prematurely. The > * call is not atomic; no spinlocks may be held. > */ > -static int __set_cpus_allowed_ptr(struct task_struct *p, > +static int __set_cpus_allowed_ptr(struct task_struct *p, bool distribute_cpus, > const struct cpumask *new_mask, bool check) > { > const struct cpumask *cpu_valid_mask = cpu_active_mask; > - unsigned int dest_cpu; > + unsigned int dest_cpu, prev_cpu; > struct rq_flags rf; > struct rq *rq; > int ret = 0; > @@ -1652,8 +1678,33 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > if (cpumask_equal(p->cpus_ptr, new_mask)) > goto out; > > - dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask); > - if (dest_cpu >= nr_cpu_ids) { > + if (!cpumask_intersects(new_mask, cpu_valid_mask)) { > + ret = -EINVAL; > + goto out; > + } > + > + prev_cpu = task_cpu(p); > + if (distribute_cpus) { > + dest_cpu = distribute_to_new_cpumask(new_mask, > + cpu_valid_mask); > + } else { > + /* > + * Can the task run on the task's current CPU? If so, we're > + * done. > + * > + * We only enable this short-circuit in the case that we're > + * not trying to distribute tasks. As we may otherwise not > + * distribute away from a loaded CPU, or make duplicate > + * assignments to it. > + */ > + if (cpumask_test_cpu(prev_cpu, new_mask)) > + dest_cpu = prev_cpu; > + else > + dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask); > + } That all seems overly complicated; what is wrong with just this: dest_cpu = cpumask_any_and_fancy(cpu_valid_mask, new_mask); I don't really buy the argument why that shortcut is problematic; it's all averages anyway, and keeping a task on a CPU where it's already running seems like a win. > + /* May have raced with cpu_down */ > + if (unlikely(dest_cpu >= nr_cpu_ids)) { > ret = -EINVAL; > goto out; > }