From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757165AbZDFQCA (ORCPT ); Mon, 6 Apr 2009 12:02:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751620AbZDFQBv (ORCPT ); Mon, 6 Apr 2009 12:01:51 -0400 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:47941 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750784AbZDFQBu (ORCPT ); Mon, 6 Apr 2009 12:01:50 -0400 Date: Mon, 6 Apr 2009 21:30:39 +0530 From: Arun R Bharadwaj To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, a.p.zijlstra@chello.nl, ego@in.ibm.com, mingo@elte.hu, andi@firstfloor.org, venkatesh.pallipadi@intel.com, vatsa@linux.vnet.ibm.com, arjan@infradead.org, svaidy@linux.vnet.ibm.com, Arun Bharadwaj Subject: Re: [v4 RFC PATCH 4/4] timers: logic to move non pinned timers Message-ID: <20090406160039.GA15269@linux.vnet.ibm.com> Reply-To: arun@linux.vnet.ibm.com References: <20090401113128.GA22478@linux.vnet.ibm.com> <20090401113738.GE22478@linux.vnet.ibm.com> <20090406051656.GA17412@linux.vnet.ibm.com> <20090406104228.GB17412@linux.vnet.ibm.com> <20090406152843.GA11645@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner [2009-04-06 17:35:09]: > Arun, > > On Mon, 6 Apr 2009, Arun R Bharadwaj wrote: > > > > - new_cpu_base = &__get_cpu_var(hrtimer_bases); > > > > +again: > > > > + new_cpu_base = &per_cpu(hrtimer_bases, cpu); > > > > new_base = &new_cpu_base->clock_base[base->index]; > > > > > > > > if (base != new_base) { > > > > @@ -220,6 +242,32 @@ switch_hrtimer_base(struct hrtimer *time > > > > spin_unlock(&base->cpu_base->lock); > > > > spin_lock(&new_base->cpu_base->lock); > > > > timer->base = new_base; > > > > + > > > > + if (cpu == preferred_cpu) { > > > > + /* Calculate clock monotonic expiry time */ > > > > + ktime_t expires = ktime_sub(hrtimer_get_expires(timer), > > > > + new_base->offset); > > > > + > > > > + /* > > > > + * Get the next event on target cpu from the > > > > + * clock events layer. > > > > + * This covers the highres=off nohz=on case as well. > > > > + */ > > > > + ktime_t next = clockevents_get_next_event(cpu); > > > > + > > > > + ktime_t delta = ktime_sub(expires, next); > > > > + > > > > + /* > > > > + * We do not migrate the timer when it is expiring > > > > + * before the next event on the target cpu because > > > > + * we cannot reprogram the target cpu hardware and > > > > + * we would cause it to fire late. > > > > + */ > > > > + if (delta.tv64 < 0) { > > > > + cpu = smp_processor_id(); > > > > > > You are missing a small but fatal detail here: You hold > > > new_base->cpu_base->lock. So you need to do: > > > > > > > I just moved the if block.. if (cpu==preferred_cpu) above the base > > locking part to avoid the extra unlocking. > > That's not a good idea. You want to look at the next event with the > base lock of the other cpu held. That prevents that expires the first > pending timer right after you checked next_event and before you queue > your timer, which then might become the first timer to expire but you > can't reprogram the clock event device on the other cpu. > Okay... I understand. Thanks for the explanation :) Will post all the changes together in a separate thread. --arun > Thanks, > > tglx