From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756088AbeEIGpZ (ORCPT ); Wed, 9 May 2018 02:45:25 -0400 Received: from lgeamrelo11.lge.com ([156.147.23.51]:42183 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753339AbeEIGpY (ORCPT ); Wed, 9 May 2018 02:45:24 -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 From: Byungchul Park To: peterz@infradead.org, mingo@kernel.org, rostedt@goodmis.org Cc: tglx@linutronix.de, raistlin@linux.it, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, bristot@redhat.com, kernel-team@lge.com Subject: [RESEND PATCH v11 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Date: Wed, 9 May 2018 15:44:22 +0900 Message-Id: <1525848263-10958-2-git-send-email-byungchul.park@lge.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1525848263-10958-1-git-send-email-byungchul.park@lge.com> References: <1525848263-10958-1-git-send-email-byungchul.park@lge.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It would be better to try to check other siblings first if SD_PREFER_SIBLING is flaged when pushing tasks - migration. 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