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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 3E3EDC606D4 for ; Tue, 9 Jul 2019 05:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21D5821707 for ; Tue, 9 Jul 2019 05:59:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727242AbfGIF7N (ORCPT ); Tue, 9 Jul 2019 01:59:13 -0400 Received: from lgeamrelo11.lge.com ([156.147.23.51]:49027 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726917AbfGIF7N (ORCPT ); Tue, 9 Jul 2019 01:59:13 -0400 Received: from unknown (HELO lgemrelse6q.lge.com) (156.147.1.121) by 156.147.23.51 with ESMTP; 9 Jul 2019 14:59:09 +0900 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.222.33) by 156.147.1.121 with ESMTP; 9 Jul 2019 14:59:09 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Tue, 9 Jul 2019 14:58:16 +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: <20190709055815.GA19459@X58A-UD3R> References: <1562565609-12482-1-git-send-email-byungchul.park@lge.com> <20190708125013.GG26519@linux.ibm.com> <20190708130359.GA42888@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190708130359.GA42888@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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. I thought only difference between them is a level of urgency. I might be wrong. It would be appreciated if you let me know if I miss something. And it's ok even if the patch is turned down based on your criteria. :) Thanks, Byungchul > Joel > > > > Thanx, Paul > > > > > The function for setting jiffies_to_sched_qs, > > > adjust_jiffies_till_sched_qs() will be called only if > > > the value from sysfs != ULONG_MAX. And the value won't be adjusted > > > unlike first/next fqs jiffies. > > > > > > While at it, changed the positions of two module_param()s downward. > > > > > > Signed-off-by: Byungchul Park > > > --- > > > kernel/rcu/tree.c | 22 ++++++++++++++++++++-- > > > 1 file changed, 20 insertions(+), 2 deletions(-) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index a2f8ba2..a28e2fe 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -422,9 +422,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > > * quiescent-state help from rcu_note_context_switch(). > > > */ > > > static ulong jiffies_till_sched_qs = ULONG_MAX; > > > -module_param(jiffies_till_sched_qs, ulong, 0444); > > > static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */ > > > -module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */ > > > > > > /* > > > * Make sure that we give the grace-period kthread time to detect any > > > @@ -450,6 +448,18 @@ static void adjust_jiffies_till_sched_qs(void) > > > WRITE_ONCE(jiffies_to_sched_qs, j); > > > } > > > > > > +static int param_set_sched_qs_jiffies(const char *val, const struct kernel_param *kp) > > > +{ > > > + ulong j; > > > + int ret = kstrtoul(val, 0, &j); > > > + > > > + if (!ret && j != ULONG_MAX) { > > > + WRITE_ONCE(*(ulong *)kp->arg, j); > > > + adjust_jiffies_till_sched_qs(); > > > + } > > > + return ret; > > > +} > > > + > > > static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp) > > > { > > > ulong j; > > > @@ -474,6 +484,11 @@ static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param > > > return ret; > > > } > > > > > > +static struct kernel_param_ops sched_qs_jiffies_ops = { > > > + .set = param_set_sched_qs_jiffies, > > > + .get = param_get_ulong, > > > +}; > > > + > > > static struct kernel_param_ops first_fqs_jiffies_ops = { > > > .set = param_set_first_fqs_jiffies, > > > .get = param_get_ulong, > > > @@ -484,8 +499,11 @@ static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param > > > .get = param_get_ulong, > > > }; > > > > > > +module_param_cb(jiffies_till_sched_qs, &sched_qs_jiffies_ops, &jiffies_till_sched_qs, 0644); > > > module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644); > > > module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644); > > > + > > > +module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */ > > > module_param(rcu_kick_kthreads, bool, 0644); > > > > > > static void force_qs_rnp(int (*f)(struct rcu_data *rdp)); > > > -- > > > 1.9.1 > > > > >