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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 C8AE5C46466 for ; Mon, 5 Oct 2020 15:10:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E0962085B for ; Mon, 5 Oct 2020 15:10:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="D1kHEnen" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726792AbgJEPKD (ORCPT ); Mon, 5 Oct 2020 11:10:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726760AbgJEPJ6 (ORCPT ); Mon, 5 Oct 2020 11:09:58 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 239C2C0613CE for ; Mon, 5 Oct 2020 08:09:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=ib/vSJZXe359LI8VEGBEO/Vt7X2CKf1PQh+C2xgwOek=; b=D1kHEnenXlQR/bUAlzRe9DtGu+ teTTDWEoQpi1eBnPgWF00XvURxecroPyonTQzkkGyT6zabc8DYthVrxuaTWR6UEnFTHx69htYXMFj rhCW+0xMt7sXsV5l9u8ib6X7LwVlHb8WoyK1WgIl9yuYJrotdPs2/MCuIT5nrXnjhIQWSLFqVLCTE 675WMls/t/4CeJfe9PE4X/TnOygMlLtPYHxXVXV+/tJAy2+35IFoo7lmAjS6aL8rxXrbgA87jN14B iQfVo6yqqS1IZTUzSYILJNRuBMaapxuio3LJMl7ofJD40yF8bZltwPpe2E7aHDStFcSavcTw8+3uy oVAVW9gQ==; 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 1kPS7W-0008PW-C5; Mon, 05 Oct 2020 15:09:46 +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 7165830769C; Mon, 5 Oct 2020 17:09:43 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id EA60F29A897BD; Mon, 5 Oct 2020 17:09:42 +0200 (CEST) Message-ID: <20201005150922.156231026@infradead.org> User-Agent: quilt/0.66 Date: Mon, 05 Oct 2020 16:57:29 +0200 From: Peter Zijlstra To: tglx@linutronix.de, mingo@kernel.org Cc: linux-kernel@vger.kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com, peterz@infradead.org, valentin.schneider@arm.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org Subject: [PATCH -v2 12/17] sched,rt: Use cpumask_any*_distribute() References: <20201005145717.346020688@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Replace a bunch of cpumask_any*() instances with cpumask_any*_distribute(), by injecting this little bit of random in cpu selection, we reduce the chance two competing balance operations working off the same lowest_mask pick the same CPU. Signed-off-by: Peter Zijlstra (Intel) --- include/linux/cpumask.h | 6 ++++++ kernel/sched/cpupri.c | 4 ++-- kernel/sched/deadline.c | 2 +- kernel/sched/rt.c | 6 +++--- lib/cpumask.c | 18 ++++++++++++++++++ 5 files changed, 30 insertions(+), 6 deletions(-) --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -199,6 +199,11 @@ static inline int cpumask_any_and_distri return cpumask_next_and(-1, src1p, src2p); } +static inline int cpumask_any_distribute(const struct cpumask *srcp) +{ + return cpumask_first(srcp); +} + #define for_each_cpu(cpu, mask) \ for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask) #define for_each_cpu_not(cpu, mask) \ @@ -252,6 +257,7 @@ int cpumask_any_but(const struct cpumask unsigned int cpumask_local_spread(unsigned int i, int node); int cpumask_any_and_distribute(const struct cpumask *src1p, const struct cpumask *src2p); +int cpumask_any_distribute(const struct cpumask *srcp); /** * for_each_cpu - iterate over every cpu in a mask --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2001,7 +2001,7 @@ static int find_later_rq(struct task_str if (this_cpu != -1) return this_cpu; - cpu = cpumask_any(later_mask); + cpu = cpumask_any_distribute(later_mask); if (cpu < nr_cpu_ids) return cpu; --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1752,8 +1752,8 @@ static int find_lowest_rq(struct task_st return this_cpu; } - best_cpu = cpumask_first_and(lowest_mask, - sched_domain_span(sd)); + best_cpu = cpumask_any_and_distribute(lowest_mask, + sched_domain_span(sd)); if (best_cpu < nr_cpu_ids) { rcu_read_unlock(); return best_cpu; @@ -1770,7 +1770,7 @@ static int find_lowest_rq(struct task_st if (this_cpu != -1) return this_cpu; - cpu = cpumask_any(lowest_mask); + cpu = cpumask_any_distribute(lowest_mask); if (cpu < nr_cpu_ids) return cpu; --- a/lib/cpumask.c +++ b/lib/cpumask.c @@ -267,3 +267,21 @@ int cpumask_any_and_distribute(const str return next; } EXPORT_SYMBOL(cpumask_any_and_distribute); + +int cpumask_any_distribute(const struct cpumask *srcp) +{ + int next, prev; + + /* NOTE: our first selection will skip 0. */ + prev = __this_cpu_read(distribute_cpu_mask_prev); + + next = cpumask_next(prev, srcp); + if (next >= nr_cpu_ids) + next = cpumask_first(srcp); + + if (next < nr_cpu_ids) + __this_cpu_write(distribute_cpu_mask_prev, next); + + return next; +} +EXPORT_SYMBOL(cpumask_any_distribute);