From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758961Ab3KMR06 (ORCPT ); Wed, 13 Nov 2013 12:26:58 -0500 Received: from terminus.zytor.com ([198.137.202.10]:52933 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755997Ab3KMR0X (ORCPT ); Wed, 13 Nov 2013 12:26:23 -0500 Date: Wed, 13 Nov 2013 09:25:41 -0800 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, torvalds@linux-foundation.org, pjt@google.com, peterz@infradead.org, akpm@linux-foundation.org, tglx@linutronix.de, kosaki.motohiro@jp.fujitsu.com, lwoodman@redhat.com Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, peterz@infradead.org, pjt@google.com, akpm@linux-foundation.org, tglx@linutronix.de, kosaki.motohiro@jp.fujitsu.com, lwoodman@redhat.com In-Reply-To: <20131111172925.GG26898@twins.programming.kicks-ass.net> References: <20131111172925.GG26898@twins.programming.kicks-ass.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched: Optimize task_sched_runtime() Git-Commit-ID: 911b2898b3c9fe0048e9485ad1629ed4fce330fd X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.1 (terminus.zytor.com [127.0.0.1]); Wed, 13 Nov 2013 09:25:47 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 911b2898b3c9fe0048e9485ad1629ed4fce330fd Gitweb: http://git.kernel.org/tip/911b2898b3c9fe0048e9485ad1629ed4fce330fd Author: Peter Zijlstra AuthorDate: Mon, 11 Nov 2013 18:21:56 +0100 Committer: Ingo Molnar CommitDate: Wed, 13 Nov 2013 13:33:54 +0100 sched: Optimize task_sched_runtime() Large multi-threaded apps like to hit this using do_sys_times() and then queue up on the rq->lock. Avoid when possible. Larry reported ~20% performance increase his test case. Reported-by: Larry Woodman Suggested-by: Paul Turner Signed-off-by: Peter Zijlstra Cc: KOSAKI Motohiro Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/r/20131111172925.GG26898@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1deccd7..c180860 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2253,6 +2253,20 @@ unsigned long long task_sched_runtime(struct task_struct *p) struct rq *rq; u64 ns = 0; +#if defined(CONFIG_64BIT) && defined(CONFIG_SMP) + /* + * 64-bit doesn't need locks to atomically read a 64bit value. + * So we have a optimization chance when the task's delta_exec is 0. + * Reading ->on_cpu is racy, but this is ok. + * + * If we race with it leaving cpu, we'll take a lock. So we're correct. + * If we race with it entering cpu, unaccounted time is 0. This is + * indistinguishable from the read occurring a few cycles earlier. + */ + if (!p->on_cpu) + return p->se.sum_exec_runtime; +#endif + rq = task_rq_lock(p, &flags); ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq); task_rq_unlock(rq, p, &flags);