From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3BC1ECDFB3 for ; Tue, 17 Jul 2018 09:11:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A0C7C21470 for ; Tue, 17 Jul 2018 09:11:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A0C7C21470 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729669AbeGQJmz (ORCPT ); Tue, 17 Jul 2018 05:42:55 -0400 Received: from terminus.zytor.com ([198.137.202.136]:41725 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728089AbeGQJmz (ORCPT ); Tue, 17 Jul 2018 05:42:55 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w6H9BBaN1458641 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 17 Jul 2018 02:11:11 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w6H9BAA21458638; Tue, 17 Jul 2018 02:11:10 -0700 Date: Tue, 17 Jul 2018 02:11:10 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: "tip-bot for Steven Rostedt (VMware)" Message-ID: Cc: hpa@zytor.com, rostedt@goodmis.org, mingo@kernel.org, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, joel@joelfernandes.org, linux-kernel@vger.kernel.org Reply-To: linux-kernel@vger.kernel.org, joel@joelfernandes.org, tglx@linutronix.de, paulmck@linux.vnet.ibm.com, mingo@kernel.org, rostedt@goodmis.org, hpa@zytor.com In-Reply-To: <20180523063815.198302-2-joel@joelfernandes.org> References: <20180523063815.198302-2-joel@joelfernandes.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:core/rcu] rcu: Speed up calling of RCU tasks callbacks Git-Commit-ID: c03be752d39dc64dcfda0ac8ce87fb10b1ee5621 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c03be752d39dc64dcfda0ac8ce87fb10b1ee5621 Gitweb: https://git.kernel.org/tip/c03be752d39dc64dcfda0ac8ce87fb10b1ee5621 Author: Steven Rostedt (VMware) AuthorDate: Thu, 24 May 2018 18:49:46 -0400 Committer: Paul E. McKenney CommitDate: Thu, 12 Jul 2018 15:39:21 -0700 rcu: Speed up calling of RCU tasks callbacks Joel Fernandes found that the synchronize_rcu_tasks() was taking a significant amount of time. He demonstrated it with the following test: # cd /sys/kernel/tracing # while [ 1 ]; do x=1; done & # echo '__schedule_bug:traceon' > set_ftrace_filter # time echo '!__schedule_bug:traceon' > set_ftrace_filter; real 0m1.064s user 0m0.000s sys 0m0.004s Where it takes a little over a second to perform the synchronize, because there's a loop that waits 1 second at a time for tasks to get through their quiescent points when there's a task that must be waited for. After discussion we came up with a simple way to wait for holdouts but increase the time for each iteration of the loop but no more than a full second. With the new patch we have: # time echo '!__schedule_bug:traceon' > set_ftrace_filter; real 0m0.131s user 0m0.000s sys 0m0.004s Which drops it down to 13% of what the original wait time was. Link: http://lkml.kernel.org/r/20180523063815.198302-2-joel@joelfernandes.org Reported-by: Joel Fernandes (Google) Suggested-by: Joel Fernandes (Google) Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Paul E. McKenney --- kernel/rcu/update.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 5783bdf86e5a..4c7c49c106ee 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -668,6 +668,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) struct rcu_head *list; struct rcu_head *next; LIST_HEAD(rcu_tasks_holdouts); + int fract; /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ housekeeping_affine(current, HK_FLAG_RCU); @@ -749,13 +750,25 @@ static int __noreturn rcu_tasks_kthread(void *arg) * holdouts. When the list is empty, we are done. */ lastreport = jiffies; - while (!list_empty(&rcu_tasks_holdouts)) { + + /* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/ + fract = 10; + + for (;;) { bool firstreport; bool needreport; int rtst; struct task_struct *t1; - schedule_timeout_interruptible(HZ); + if (list_empty(&rcu_tasks_holdouts)) + break; + + /* Slowly back off waiting for holdouts */ + schedule_timeout_interruptible(HZ/fract); + + if (fract > 1) + fract--; + rtst = READ_ONCE(rcu_task_stall_timeout); needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);