From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755559AbZDFK6q (ORCPT ); Mon, 6 Apr 2009 06:58:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755269AbZDFK6h (ORCPT ); Mon, 6 Apr 2009 06:58:37 -0400 Received: from www.tglx.de ([62.245.132.106]:45699 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755218AbZDFK6g (ORCPT ); Mon, 6 Apr 2009 06:58:36 -0400 Date: Mon, 6 Apr 2009 12:56:17 +0200 (CEST) From: Thomas Gleixner To: Arun R Bharadwaj 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 Subject: Re: [v4 RFC PATCH 4/4] timers: logic to move non pinned timers In-Reply-To: <20090406104228.GB17412@linux.vnet.ibm.com> Message-ID: 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> 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 Arun, On Mon, 6 Apr 2009, Arun R Bharadwaj wrote: > > +ktime_t clockevents_get_next_event(int cpu) > +{ > + struct tick_device *td; > + struct clock_event_device *dev; > + > + td = &per_cpu(tick_cpu_device, cpu); > + dev = td->evtdev; > + > + return dev->next_event; > +} > + Preferrably this function should be in the clock events code and a stub inline function which returns KTIME_MAX for non clock events archs is probably necessary as well. > /* > * Switch the timer base to the current CPU when possible. > */ > @@ -198,8 +211,17 @@ switch_hrtimer_base(struct hrtimer *time > { > struct hrtimer_clock_base *new_base; > struct hrtimer_cpu_base *new_cpu_base; > + int cpu, preferred_cpu = -1; > + > + cpu = smp_processor_id(); > + if (get_sysctl_timer_migration() && !pinned && idle_cpu(cpu)) { > + preferred_cpu = get_nohz_load_balancer(); > + if (preferred_cpu >= 0) > + cpu = preferred_cpu; > + } > > - 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: spin_unlock(&new_base->cpu_base->lock); spin_lock(&base->cpu_base->lock); > + goto again; > + } Also you need to move > timer->base = new_base; here to avoid a stale timer->base setting. > + } > } > return new_base; > } Thanks, tglx