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

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Date:	Mon, 13 Sep 2010 14:46:32 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Vasily Khoruzhick <anarsoul@...il.com>
Cc:	intel-gfx@...ts.freedesktop.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Interrupt latency on some 945GM platforms

On Tue, 14 Sep 2010 00:41:18 +0300
Vasily Khoruzhick <anarsoul@...il.com> wrote:

> В сообщении от 14 of September 2010 00:19:55 автор Jesse Barnes написал:
> > On Tue, 14 Sep 2010 00:10:08 +0300
> > 
> > Vasily Khoruzhick <anarsoul@...il.com> wrote:
> > > В сообщении от 13 of September 2010 23:44:41 автор Jesse Barnes написал:
> > > > I remember seeing a similar problem on an Eee PC I had; it seemed to be
> > > > timer/interrupt related somehow.  If I booted with clocksource=tsc
> > > > (or maybe it was pit) I got nice smooth animations, but if I used the
> > > > HPET things were really slow.
> > > > 
> > > > Does the same work for you?
> > > 
> > > Yeah, it works for me (will use it as temporary workaround). But it
> > > definitely is not clean solution, as I can't use nohz mode with tsc
> > > clocksource :)
> > 
> > Thomas, does this ring any bells for you?
> > 
> > I think the root symptom of the issue is that we get a much reduced i915
> > interrupt frequency (or no interrupts) on some 945GM platforms when
> > using HPET as our clock source.
> > 
> > In fact, on the platform I tested, it seemed that the i915 IRQs wouldn't
> > generate interrupts at all when HPET was used.  But shaking the mouse or
> > generating network traffic was enough to get i915 interrupts coming in,
> > even though neither of those interrupts were shared with the i915
> > device.
> > 
> > Here's hoping you have some ideas to try...
> > 
> > Thanks,
> 
> Jesse, is it possible to disable wait for vsync somehow? cpufreq is not 
> working for me with nohz=no for some reason, as result cpu temperature and 
> power usage are higher. I prefer to see tearing but with low power usage and 
> without jerky keyboard :)

Yes, you can set vblank_mode=0 in your environment or drirc.  At least
I think 0 is no vsync. :)

-- 
Jesse Barnes, Intel Open Source Technology Center
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