From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751297AbdJWIok (ORCPT ); Mon, 23 Oct 2017 04:44:40 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:37043 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751178AbdJWIoj (ORCPT ); Mon, 23 Oct 2017 04:44:39 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Mon, 23 Oct 2017 17:44:32 +0900 From: Byungchul Park To: peterz@infradead.org, mingo@kernel.org, rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org, juri.lelli@gmail.com, kernel-team@lge.com Subject: Re: [RESEND PATCH v11 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Message-ID: <20171023084432.GL3310@X58A-UD3R> References: <1507617474-21816-1-git-send-email-byungchul.park@lge.com> <1507617474-21816-2-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1507617474-21816-2-git-send-email-byungchul.park@lge.com> 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 Tue, Oct 10, 2017 at 03:37:53PM +0900, Byungchul Park wrote: > It would be better to try to check other siblings first if > SD_PREFER_SIBLING is flaged when pushing tasks - migration. Is there any opinion about this patch? Could you consider this? > Suggested-by: Peter Zijlstra > Signed-off-by: Byungchul Park > Acked-by: Juri Lelli > --- > kernel/sched/deadline.c | 82 ++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 75 insertions(+), 7 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 0223694..d619c07 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu > > static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl); > > +/* > + * Find the first cpu in: mask & sd & ~prefer > + */ > +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; > + > + for_each_cpu(cpu, mask) { > + 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)) > @@ -1376,15 +1399,37 @@ static int find_later_rq(struct task_struct *task) > return this_cpu; > } > > - best_cpu = cpumask_first_and(later_mask, > - sched_domain_span(sd)); > /* > - * Last chance: if a cpu being in both later_mask > - * and current sd span is valid, that becomes our > - * choice. Of course, the latest possible cpu is > - * already under consideration through later_mask. > + * If a cpu exists that is in the later_mask and > + * the current sd span, but not in the prefer sd > + * span, then that becomes our choice. > + * > + * Of course, the latest possible cpu is already > + * under consideration through later_mask. > */ > + best_cpu = find_cpu(later_mask, sd, prefer); > + > if (best_cpu < nr_cpu_ids) { > + /* > + * If current domain is SD_PREFER_SIBLING > + * flaged, we have to try to check other > + * siblings first. > + */ > + if (sd->flags & SD_PREFER_SIBLING) { > + prefer = sd; > + > + /* > + * fallback_cpu should be one > + * in the closest domain among > + * SD_PREFER_SIBLING domains, > + * in case that more than one > + * SD_PREFER_SIBLING domains > + * exist in the hierachy. > + */ > + if (fallback_cpu == -1) > + fallback_cpu = best_cpu; > + continue; > + } > rcu_read_unlock(); > return best_cpu; > } > @@ -1393,6 +1438,29 @@ static int find_later_rq(struct task_struct *task) > rcu_read_unlock(); > > /* > + * If fallback_cpu is valid, all our guesses failed *except* for > + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu. > + * > + * XXX: Consider the following example, 4 cores SMT2 system: > + * > + * LLC [0 - 7] > + * SMT [0 1][2 3][4 5][6 7] > + * o x o x x x x x > + * > + * where 'o': occupied and 'x': empty. > + * > + * A wakeup on cpu0 will exclude cpu1 and choose cpu3, since > + * cpu1 is in a SD_PREFER_SIBLING sd and cpu3 is not. However, > + * in this case, cpu4 would have been a better choice, since > + * cpu3 is a (SMT) thread of an already loaded core. > + * > + * Doing it 'right' is difficult and expensive. The current > + * solution is an acceptable approximation. > + */ > + if (fallback_cpu != -1) > + return fallback_cpu; > + > + /* > * At this point, all our guesses failed, we just return > * 'something', and let the caller sort the things out. > */ > -- > 1.9.1