From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751300AbdHDFRg (ORCPT ); Fri, 4 Aug 2017 01:17:36 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:53700 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbdHDFRf (ORCPT ); Fri, 4 Aug 2017 01:17:35 -0400 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Fri, 4 Aug 2017 14:16:26 +0900 From: Byungchul Park To: Peter Zijlstra Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, rostedt@goodmis.org, bristot@redhat.com, kernel-team@lge.com Subject: Re: [PATCH v5 3/4] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Message-ID: <20170804051626.GP20323@X58A-UD3R> References: <1495504859-10960-1-git-send-email-byungchul.park@lge.com> <1495504859-10960-4-git-send-email-byungchul.park@lge.com> <20170803120334.dogbysvrfeoseu6v@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170803120334.dogbysvrfeoseu6v@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 03, 2017 at 02:03:34PM +0200, Peter Zijlstra wrote: > This one I'm not sure on.. at the very least we should exclude all of > the prefer sibling domain when we do the next domain, and if there are > multiple prefer sibling levels, we should only pick the first > fallback_cpu -- there is no point is overriding it with a possible CPU > further away. I agree. > I implemented that below -- although the find_cpu() function is really > rather horrible. > > But still this isn't quite right, because when we consider this for SMT > (as was the intent here) we'll happily occupy a full sibling core over > finding an empty one. > > Now, the problem is that actually doing the right thing quickly ends up > very expensive, we'd have to scan the entire cache domain at least once, > so maybe this is good enough.. no idea :/ > > > --- > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1793,12 +1793,35 @@ static struct task_struct *pick_earliest > > static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl); > > +/* > + * Find the first cpu in: mask & sd & ~prefer ^ Yes, I missed it. > + */ > +static int find_cpu(const struct cpumask *mask, > + const struct sched_domain *sd, > + const struct sched_domain *prefer) > +{ > + const struct cpumask *sds = sched_domain_span(sd); > + const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL; > + int cpu = -1; > + > + while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) { > + if (!cpumask_test_cpu(cpu, sds)) > + continue; > + if (ps && cpumask_test_cpu(cpu, ps)) > + continue; > + break; > + } > + > + return cpu; > +} > + > static int find_later_rq(struct task_struct *task) > { > - struct sched_domain *sd; > + struct sched_domain *sd, *prefer = NULL; > struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl); > int this_cpu = smp_processor_id(); > int cpu = task_cpu(task); > + int fallback_cpu = -1; > > /* Make sure the mask is initialized first */ > if (unlikely(!later_mask)) > @@ -1850,8 +1873,7 @@ static int find_later_rq(struct task_str > return this_cpu; > } > > - best_cpu = cpumask_first_and(later_mask, > - sched_domain_span(sd)); > + best_cpu = find_cpu(later_mask, sd, prefer); > /* > * Last chance: if a cpu being in both later_mask > * and current sd span is valid, that becomes our > @@ -1859,6 +1881,17 @@ static int find_later_rq(struct task_str > * already under consideration through later_mask. > */ > if (best_cpu < nr_cpu_ids) { > + /* > + * If current domain is SD_PREFER_SIBLING > + * flaged, we have to get more chances to > + * check other siblings. > + */ > + if (sd->flags & SD_PREFER_SIBLING) { > + prefer = sd; > + if (fallback_cpu == -1) ^ I like the 'if' statement. I should have done this. > + fallback_cpu = best_cpu; > + continue; > + } > rcu_read_unlock(); > return best_cpu; > } Thank you.