linux-kernel - Re: nohz and strange sleep latencies

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Message-ID: <20071124224013.GB1544@elf.ucw.cz>
Date:	Sat, 24 Nov 2007 23:40:13 +0100
From:	Pavel Machek <pavel@....cz>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: nohz and strange sleep latencies

Hi!

> > > but perhaps somehow we miss this fact and fail to turn off the lapic 
> > > clockevents drivers?
> > 
> > Ok, I guess I'm lost. If I offline second CPU, I immediately get
> > 1000Hz timer tick... is that expected?
> 
> Hmm. No. I have no idea why this is happening.
> 
> 34196 total events, 55.083 events/sec
> echo 0 >/sys/devices/system/cpu/cpu1/online
> 36073 total events, 54.679 events/sec

Digging into process_32|64.c...

64:
        while (1) {
                while (!need_resched()) {
                        void (*idle)(void);

                        if (__get_cpu_var(cpu_idle_state))
                                __get_cpu_var(cpu_idle_state) = 0;

                        tick_nohz_stop_sched_tick();

32:
        while (1) {
                tick_nohz_stop_sched_tick();
                while (!need_resched()) {
                        void (*idle)(void);

                        if (__get_cpu_var(cpu_idle_state))
                                __get_cpu_var(cpu_idle_state) = 0;

...eek? Which one is wrong?
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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