linux-kernel - Re: nohz and strange sleep latencies

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Date:	Tue, 20 Nov 2007 23:52:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: nohz and strange sleep latencies


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Tue, 20 Nov 2007, Ingo Molnar wrote:
> > 
> > * Pavel Machek <pavel@....cz> wrote:
> > 
> > > > and send us the output? (Enabling CONFIG_TIMER_STATS, 
> > > > CONFIG_SCHED_DEBUG and CONFIG_SCHEDSTATS would maximize the amount 
> > > > of information.)
> > > 
> > > This was w/o hpet=disable . Do you want me to test with hpet=disable?
> > 
> > no, this is fine. You've got a hpet clockevents driver and two lapic 
> > drivers:
> > 
> > Clock Event Device: hpet
> >  set_next_event: hpet_legacy_next_event
> >  set_mode:       hpet_legacy_set_mode
> >  event_handler:  tick_handle_oneshot_broadcast
> > 
> > Clock Event Device: lapic
> >  set_next_event: lapic_next_event
> >  set_mode:       lapic_timer_setup
> >  event_handler:  hrtimer_interrupt
> > 
> > Clock Event Device: lapic
> >  set_next_event: lapic_next_event
> >  set_mode:       lapic_timer_setup
> >  event_handler:  hrtimer_interrupt
> > 
> > to me this has the feeling of lapic breakage in C2 mode. Does it get any 
> > better if you boot with 'nolapic'? (but that might in turn turn off 
> > high-res timers and nohz in essence) Thomas, any ideas?
> 
> Hmm, lapic is considered unstable in c2 by default. You have to tell 
> the kernel that you trust it in C2 on the command line.

yeah, i was wondering about that too. ACPI enumerated them properly at a 
certain stage:

 ACPI: CPU0 (power states: C1[C1] C2[C2] C3[C3])
 ACPI: CPU1 (power states: C1[C1] C2[C2] C3[C3])

but perhaps somehow we miss this fact and fail to turn off the lapic 
clockevents drivers?

	Ingo
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