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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 0F501C606D5 for ; Tue, 9 Jul 2019 06:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E68D5216C4 for ; Tue, 9 Jul 2019 06:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726122AbfGIGq1 (ORCPT ); Tue, 9 Jul 2019 02:46:27 -0400 Received: from lgeamrelo13.lge.com ([156.147.23.53]:57850 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725832AbfGIGq0 (ORCPT ); Tue, 9 Jul 2019 02:46:26 -0400 Received: from unknown (HELO lgeamrelo01.lge.com) (156.147.1.125) by 156.147.23.53 with ESMTP; 9 Jul 2019 15:46:24 +0900 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.222.33) by 156.147.1.125 with ESMTP; 9 Jul 2019 15:46:24 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Tue, 9 Jul 2019 15:45:31 +0900 From: Byungchul Park To: Joel Fernandes Cc: "Paul E. McKenney" , josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [PATCH] rcu: Make jiffies_till_sched_qs writable Message-ID: <20190709064531.GA15734@X58A-UD3R> References: <1562565609-12482-1-git-send-email-byungchul.park@lge.com> <20190708125013.GG26519@linux.ibm.com> <20190708130359.GA42888@google.com> <20190709055815.GA19459@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190709055815.GA19459@X58A-UD3R> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 09, 2019 at 02:58:16PM +0900, Byungchul Park wrote: > On Mon, Jul 08, 2019 at 09:03:59AM -0400, Joel Fernandes wrote: > > > Actually, the intent was to only allow this to be changed at boot time. > > > Of course, if there is now a good reason to adjust it, it needs > > > to be adjustable. So what situation is making you want to change > > > jiffies_till_sched_qs at runtime? To what values is it proving useful > > > to adjust it? What (if any) relationships between this timeout and the > > > various other RCU timeouts need to be maintained? What changes to > > > rcutorture should be applied in order to test the ability to change > > > this at runtime? > > > > I am also interested in the context, are you changing it at runtime for > > experimentation? I recently was doing some performance experiments and it is > > quite interesting how reducing this value can shorten grace period times :) > > Hi Joel, > > I've read a thread talking about your experiment to see how the grace > periods change depending on the tunnable variables which was interesting > to me. While reading it, I found out jiffies_till_sched_qs is not > tunnable at runtime unlike jiffies_till_{first,next}_fqs which looks > like non-sense to me that's why I tried this patch. :) > > Hi Paul, > > IMHO, as much as we want to tune the time for fqs to be initiated, we > can also want to tune the time for the help from scheduler to start. Let me mention one more thing here... This is about jiffies_till_sched_qs, I think, used to directly set jiffies_to_sched_qs. > I thought only difference between them is a level of urgency. Of course, they are coupled in case jiffies_to_sched_qs is calculated from jiffies_till_{first,next}_fqs though, I'm just talking about its original motivation or concept. Thanks, Byungchul