Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760130Ab0FQOMu (ORCPT ); Thu, 17 Jun 2010 10:12:50 -0400 Received: from www.tglx.de ([62.245.132.106]:36458 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752999Ab0FQOMt (ORCPT ); Thu, 17 Jun 2010 10:12:49 -0400 Date: Thu, 17 Jun 2010 16:11:59 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Mike Galbraith , Jiri Kosina , Brian Bloniarz , Chris Wedgwood , Linus Torvalds , Greg KH , Alan Cox , OGAWA Hirofumi , Jef Driesen , linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: Slow pty's (was Re: libdivecomputer interfaces?) In-Reply-To: <1276781044.27822.309.camel@twins> Message-ID: References: <20100610181042.GA19210@puku.stupidest.org> <4C116652.8010408@athenacr.com> <1276701411.30669.6.camel@marge.simson.net> <1276756770.8248.20.camel@marge.simson.net> <1276758038.9628.1.camel@marge.simson.net> <1276771844.8121.14.camel@marge.simson.net> <1276781044.27822.309.camel@twins> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2421 Lines: 76 On Thu, 17 Jun 2010, Peter Zijlstra wrote: > On Thu, 2010-06-17 at 12:50 +0200, Mike Galbraith wrote: > > > sched: do not ratelimit NOHZ when the tick is stopped. > > > > Chris Wedgwood reports that 39c0cbe sched: Rate-limit nohz causes a serial > > console regression, unresponsiveness, and indeed it does. The below fixes > > it by not skipping out when the tick has been stopped. > > > > Tested that the throughput benefit of ratelimiting is still intact. It is. > > > > Signed-off-by: Mike Galbraith > > Reported-by: Chris Wedgwood > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index 5f171f0..83c5129 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -315,7 +315,7 @@ void tick_nohz_stop_sched_tick(int inidle) > > goto end; > > } > > > > - if (nohz_ratelimit(cpu)) > > + if (!ts->tick_stopped && nohz_ratelimit(cpu)) > > goto end; > > > > ts->idle_calls++; > > > > > Humm,. the code around there suggests something like the below, but I > must admit its been a while since I really read all that nohz stuff, > Thomas, any preferences? The version below is better as it solves the problem and follows the nohz_ratelimit() advise even in the case where it changes after the tick has been stopped. Thanks, tglx > --- > kernel/time/tick-sched.c | 5 +---- > 1 files changed, 1 insertions(+), 4 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 5f171f0..e0707ea 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -315,9 +315,6 @@ void tick_nohz_stop_sched_tick(int inidle) > goto end; > } > > - if (nohz_ratelimit(cpu)) > - goto end; > - > ts->idle_calls++; > /* Read jiffies and the time when jiffies were updated last */ > do { > @@ -328,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidle) > } while (read_seqretry(&xtime_lock, seq)); > > if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) || > - arch_needs_cpu(cpu)) { > + arch_needs_cpu(cpu) || nohz_ratelimit(cpu)) { > next_jiffies = last_jiffies + 1; > delta_jiffies = 1; > } else { > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/