From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965365AbXDKUbh (ORCPT ); Wed, 11 Apr 2007 16:31:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965379AbXDKUbh (ORCPT ); Wed, 11 Apr 2007 16:31:37 -0400 Received: from smtp.osdl.org ([65.172.181.24]:59553 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965365AbXDKUbg (ORCPT ); Wed, 11 Apr 2007 16:31:36 -0400 Date: Wed, 11 Apr 2007 13:31:22 -0700 From: Andrew Morton To: Daniel Walker Cc: linux-kernel@vger.kernel.org, johnstul@us.ibm.com, tglx@linutronix.de, Andi Kleen Subject: Re: [PATCH] i386 tsc: remove xtime_lock'ing around cpufreq notifier Message-Id: <20070411133122.badf1c4f.akpm@linux-foundation.org> In-Reply-To: <20070411162904.232696302@mvista.com> References: <20070411162904.232696302@mvista.com> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 11 Apr 2007 09:29:04 -0700 Daniel Walker wrote: > The locking of the xtime_lock around the cpu notifier is unessesary now. At one > time the tsc was used after a frequency change for timekeeping, but the re-write > of timekeeping no longer uses the TSC unless the frequency is constant. > > The variables that are changed in this section of code had also once been used > for timekeeping, but not any longer .. > > Signed-Off-By: Daniel Walker > > --- > arch/i386/kernel/tsc.c | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) > > Index: linux-2.6.20/arch/i386/kernel/tsc.c > =================================================================== > --- linux-2.6.20.orig/arch/i386/kernel/tsc.c > +++ linux-2.6.20/arch/i386/kernel/tsc.c > @@ -200,13 +200,10 @@ time_cpufreq_notifier(struct notifier_bl > { > struct cpufreq_freqs *freq = data; > > - if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE) > - write_seqlock_irq(&xtime_lock); > - > if (!ref_freq) { > if (!freq->old){ > ref_freq = freq->new; > - goto end; > + return 0; > } > ref_freq = freq->old; > loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy; > @@ -237,9 +234,6 @@ time_cpufreq_notifier(struct notifier_bl > } > } > } > -end: > - if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE) > - write_sequnlock_irq(&xtime_lock); > > return 0; > } hm. I've been permadropping Andi's ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt-current/patches/sched-clock-share because it causes a lockup when initscripts start ondemand on my single-CPU, CONFIG_SMP=n Vaio. I don't know _why_ it locks up - I traced it down to the write_seqlock_irq() which you have just removed. But write_seqlock() doesn't loop with CONFIG_SMP=n builds, so a hang there is quite mysterious. Anyway, your patch might make that hang go away. We'll see.