From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934002AbcGKQQK (ORCPT ); Mon, 11 Jul 2016 12:16:10 -0400 Received: from foss.arm.com ([217.140.101.70]:54064 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932295AbcGKQQI (ORCPT ); Mon, 11 Jul 2016 12:16:08 -0400 Subject: Re: [PATCH v2 06/13] sched: Store maximum per-cpu capacity in root domain To: Peter Zijlstra , Morten Rasmussen References: <1466615004-3503-1-git-send-email-morten.rasmussen@arm.com> <1466615004-3503-7-git-send-email-morten.rasmussen@arm.com> <20160711101832.GN30909@twins.programming.kicks-ass.net> Cc: mingo@redhat.com, yuyang.du@intel.com, vincent.guittot@linaro.org, mgalbraith@suse.de, linux-kernel@vger.kernel.org From: Dietmar Eggemann Message-ID: <5783C646.5050606@arm.com> Date: Mon, 11 Jul 2016 17:16:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <20160711101832.GN30909@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/07/16 11:18, Peter Zijlstra wrote: > On Wed, Jun 22, 2016 at 06:03:17PM +0100, Morten Rasmussen wrote: >> @@ -6905,11 +6906,19 @@ static int build_sched_domains(const struct cpumask *cpu_map, >> /* Attach the domains */ >> rcu_read_lock(); >> for_each_cpu(i, cpu_map) { >> + rq = cpu_rq(i); >> sd = *per_cpu_ptr(d.sd, i); >> cpu_attach_domain(sd, d.rd, i); >> + >> + if (rq->cpu_capacity_orig > rq->rd->max_cpu_capacity) >> + rq->rd->max_cpu_capacity = rq->cpu_capacity_orig; >> } > > Should you not set that _before_ cpu_attach_domain(), such that the > state is up-to-date when its published? yes, much better. > Also, since its lockless, should we not use {READ,WRITE}_ONCE() with it? You mean for rq->rd->max_cpu_capacity ? IMHO, there is a data dependency between the read and the write and the code only runs on one cpu. I assume here that this is related to item 2 'Overlapping loads and stores within a particular CPU ...' in GUARANTEES of doc/Documentation/memory-barriers.txt. Do I miss something? >> rcu_read_unlock(); >> >> + if (rq) >> + pr_info("span: %*pbl (max cpu_capacity = %lu)\n", >> + cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity); >> + > > While a single statement, it is multi line, please add brackets. OK. > >> ret = 0; >> error: