linux-kernel - Re: Interrupt latency on some 945GM platforms

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Date:	Tue, 14 Sep 2010 11:52:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vasily Khoruzhick <anarsoul@...il.com>
cc:	Venkatesh Pallipadi <venki@...gle.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: Interrupt latency on some 945GM platforms

On Tue, 14 Sep 2010, Vasily Khoruzhick wrote:

> В сообщении от 14 of September 2010 03:55:32 автор Venkatesh Pallipadi 
> написал:
> 
> > Whats the clockevent in this case ("Tick Device" section of
> > /proc/timer_list). clocksource= option only changes the clocksource used
> > to maintain
> > timeofday. But, timer interrupt (clockevent) source will not change.
> > Wondering how just the clocksource change is making the diff here..
> > 
> > Also, if clocksource tsc has a higher rating than HPET. The reason
> > HPET is getting used as clocksource in the first place seems to be due
> > to TSC is not a dependable clocksource on this platform (may be it
> > stops in C3). So, I am not sure forcing it to tsc will be a good
> > thing. May be clocksource=acpi_pm is a better thing to try.
> > 
> > Thanks,
> > Venki
> 
> I investigated it a bit and found out that single nohz=off option helps. Just 
> changing clocksource doesn't help, but it works smoothly with any clocksource 
> with nohz=off. So, it seems that something wrong with intel driver while 
> system is in tickless mode. 

Can you try with NOHZ enabled and the following on the kernel command line:

    processor.max_cstate=1

Make sure that CONFIG_ACPI_PROCESSOR is set to "y" and not to "m"

If that works, then try

    processor.max_cstate=2

Thanks,

	tglx