Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760012Ab0FQNYx (ORCPT ); Thu, 17 Jun 2010 09:24:53 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:60738 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759972Ab0FQNYw convert rfc822-to-8bit (ORCPT ); Thu, 17 Jun 2010 09:24:52 -0400 Subject: Re: Slow pty's (was Re: libdivecomputer interfaces?) From: Peter Zijlstra To: Mike Galbraith Cc: Jiri Kosina , Brian Bloniarz , Chris Wedgwood , Linus Torvalds , Greg KH , Alan Cox , OGAWA Hirofumi , Jef Driesen , linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner In-Reply-To: <1276771844.8121.14.camel@marge.simson.net> 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> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 17 Jun 2010 15:24:04 +0200 Message-ID: <1276781044.27822.309.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2078 Lines: 66 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? --- 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/