linux-kernel - Re: nohz and strange sleep latencies

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Message-ID: <20071120105458.GA1597@elf.ucw.cz>
Date:	Tue, 20 Nov 2007 11:54:58 +0100
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	kernel list <linux-kernel@...r.kernel.org>, tglx@...utronix.de
Subject: Re: nohz and strange sleep latencies

Hi!
> 
> > > > 0.00user 0.00system 0.08 (0m0.081s) elapsed 3.71%CPU
> > > > 0.00user 0.00system 0.01 (0m0.013s) elapsed 23.33%CPU
> > > > 0.00user 0.00system 0.01 (0m0.019s) elapsed 15.92%CPU
> > > > 
> > > > nohz=off helps a lot. while true; do time sleep 0.0; done does not 
> > > > have unexpected latencies.
> > > 
> > > does hpet=disable on the boot line also help? (without nohz=off)
> > 
> > hpet-disable helps.. a bit. 200msec latencies are gone. (What is used 
> > for wakeups in this case?)
> > 
> > pavel@amd:~$ while true; do time sleep 0.01; done
> > 0.00user 0.00system 0.01 (0m0.013s) elapsed 22.96%CPU
> > 0.00user 0.00system 0.01 (0m0.018s) elapsed 11.05%CPU
> > 0.00user 0.00system 0.01 (0m0.013s) elapsed 15.54%CPU
> 
> could you run this while doing the sleep test:
> 
>   http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh
> 
> 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?
									Pavel

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

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