linux-kernel - Re: nohz and strange sleep latencies

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Message-Id: <200711250035.27400.rjw@sisk.pl>
Date:	Sun, 25 Nov 2007 00:35:26 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: nohz and strange sleep latencies

On Sunday, 25 of November 2007, Rafael J. Wysocki wrote:
> On Saturday, 24 of November 2007, Pavel Machek wrote:
> > 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?
> 
> Hm, it looks like you should have quoted more lines ...
> 
> In the second case (32), the tick_nohz_stop_sched_tick() seems to be
> redundant, so I bet it's this one.

OTOH, the ARM's process.c is more similar to process_32.c ...
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