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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 45953C352BE for ; Tue, 14 Apr 2020 16:20:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 314D02075E for ; Tue, 14 Apr 2020 16:20:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391356AbgDNQUH (ORCPT ); Tue, 14 Apr 2020 12:20:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:57656 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391002AbgDNQUA (ORCPT ); Tue, 14 Apr 2020 12:20:00 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7708720678; Tue, 14 Apr 2020 16:19:58 +0000 (UTC) Date: Tue, 14 Apr 2020 12:19:56 -0400 From: Steven Rostedt To: Qais Yousef Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Andrew Morton , Thomas Gleixner , Yury Norov , Paul Turner , Alexey Dobriyan , Josh Don , Pavan Kondeti , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] cpumask: Make cpumask_any() truly random Message-ID: <20200414121956.3687d6e9@gandalf.local.home> In-Reply-To: <20200414150556.10920-3-qais.yousef@arm.com> References: <20200414150556.10920-1-qais.yousef@arm.com> <20200414150556.10920-3-qais.yousef@arm.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 14 Apr 2020 16:05:54 +0100 Qais Yousef wrote: > Commit 46a87b3851f0 ("sched/core: Distribute tasks within affinity masks") > added a new cpumask_any_and_distribute() which truly returns a random > cpu within the mask. > > Previous patch renamed the function to cpumask_any_and(), so that old > users can take advantage of the new randomness behavior. > > Build up on that, and let cpumask_any() truly random too by re-using the > logic from cpumask_any_and(). > > Signed-off-by: Qais Yousef > CC: Juri Lelli > CC: Vincent Guittot > CC: Dietmar Eggemann > CC: Steven Rostedt > CC: Ben Segall > CC: Mel Gorman > CC: Andrew Morton > CC: Thomas Gleixner > CC: Yury Norov > CC: Paul Turner > CC: Alexey Dobriyan > CC: Josh Don > CC: Pavan Kondeti > CC: linux-kernel@vger.kernel.org > --- > include/linux/cpumask.h | 14 ++++++-------- > lib/cpumask.c | 24 ++++++++++++++++++++++++ > 2 files changed, 30 insertions(+), 8 deletions(-) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index e4d6d140a67c..7fb25d256043 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -194,6 +194,11 @@ static inline unsigned int cpumask_local_spread(unsigned int i, int node) > return 0; > } > > +static inline int cpumask_any(const struct cpumask *src1p) > +{ > + return 0; > +} > + > static inline int cpumask_any_and(const struct cpumask *src1p, > const struct cpumask *src2p) > { > @@ -251,6 +256,7 @@ static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp) > int cpumask_next_and(int n, const struct cpumask *, const struct cpumask *); > int cpumask_any_but(const struct cpumask *mask, unsigned int cpu); > unsigned int cpumask_local_spread(unsigned int i, int node); > +int cpumask_any(const struct cpumask *srcp); > int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p); > > /** > @@ -600,14 +606,6 @@ static inline void cpumask_copy(struct cpumask *dstp, > bitmap_copy(cpumask_bits(dstp), cpumask_bits(srcp), nr_cpumask_bits); > } > > -/** > - * cpumask_any - pick a "random" cpu from *srcp > - * @srcp: the input cpumask > - * > - * Returns >= nr_cpu_ids if no cpus set. > - */ > -#define cpumask_any(srcp) cpumask_first(srcp) > - > /** > * cpumask_first_and - return the first cpu from *srcp1 & *srcp2 > * @src1p: the first input > diff --git a/lib/cpumask.c b/lib/cpumask.c > index b527a153b023..bcac63e45374 100644 > --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -259,3 +259,27 @@ int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p) > return next; > } > EXPORT_SYMBOL(cpumask_any_and); > + > +/** > + * cpumask_any - pick a "random" cpu from *srcp > + * @srcp: the input cpumask > + * > + * Returns >= nr_cpu_ids if no cpus set. > + */ > +int cpumask_any(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); Do we care if this gets preempted and migrated to a new CPU where we read "prev" from one distribute_cpu_mask_prev on one CPU and write it to another CPU? -- Steve > + > + return next; > +} > +EXPORT_SYMBOL(cpumask_any);