Messages in this thread | | | Subject | Re: dynticks: CONFIG_VIRT_CPU_ACCOUNTING + CONFIG_CONTEXT_TRACKING breaks accounting on core2 CPUs only | From | Mike Galbraith <> | Date | Wed, 15 May 2013 06:09:15 +0200 |
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On Wed, 2013-05-15 at 02:26 +0200, Frederic Weisbecker wrote: > On Tue, May 14, 2013 at 04:07:20PM +0200, Mike Galbraith wrote: > > On Tue, 2013-05-14 at 02:57 +0200, Frederic Weisbecker wrote: > > > On Sun, May 12, 2013 at 10:17:49AM +0200, Mike Galbraith wrote: > > > > Greetings, > > > > > > > > Turning on new NO_HZ feature on my Q6600 box in master, I see that tasks > > > > accrue zero utime/stime. However, the same exact kernel on E5620 box > > > > works fine, so it would appear there's a CPU dependency somewhere. > > > > > > Ah indeed, I just managed to reproduce the same issue. > > > > > > > > > > > Is core2 expected to go dysfunctional with context tracking enabled? > > > > CONFIG_VIRT_CPU_ACCOUNTING alone works fine in 3.9-stable, turn on > > > > CONFIG_CONTEXT_TRACKING_FORCE, and CPU accounting stops working on core2 > > > > boxen only, same exact kernel continues to work just fine on E5620 > > > > (Westmere) box. > > > > > > There was no known issue with core2. The box where I'm seeing the it > > > is a Phenom quad core that had NR_CPUS=2. May be the issue is more > > > likely to happen with this low number. I don't know. > > > > > > I'm investigating further. > > > > So with CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, you can't mix sched_clock() > > (pure tsc) with local_clock()/sched_clock_cpu(cpu). The former is > > always quite a bit ahead of the later, so mixing clocks is a nogo on > > crusty old (but beloved) core2 box. > > Right I have the same issue. So let's use local_clock() everywhere here, > it takes care of unstable tsc. > > Does the following fix the issue for you?
Yeah, both can use sched_clock_cpu() instead though.
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index cc2dc3e..1ce322f 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -747,7 +748,7 @@ void arch_vtime_task_switch(struct task_struct *prev) > > write_seqlock(¤t->vtime_seqlock); > current->vtime_snap_whence = VTIME_SYS; > - current->vtime_snap = sched_clock(); > + current->vtime_snap = local_clock(); > write_sequnlock(¤t->vtime_seqlock); > } > > @@ -757,7 +758,7 @@ void vtime_init_idle(struct task_struct *t) > > write_seqlock_irqsave(&t->vtime_seqlock, flags); > t->vtime_snap_whence = VTIME_SYS; > - t->vtime_snap = sched_clock(); > + t->vtime_snap = local_clock(); > write_sequnlock_irqrestore(&t->vtime_seqlock, flags); > } >
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