linux-kernel - Re: [Intel-gfx] Interrupt latency on some 945GM platforms

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Date:	Fri, 17 Sep 2010 10:02:08 +0100
From:	Simon Farnsworth <simon.farnsworth@...lan.co.uk>
To:	intel-gfx@...ts.freedesktop.org
Cc:	Vasily Khoruzhick <anarsoul@...il.com>,
	Sitsofe Wheeler <sitsofe@...oo.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [Intel-gfx] Interrupt latency on some 945GM platforms

On Thursday 16 September 2010, Vasily Khoruzhick <anarsoul@...il.com> wrote:
> В сообщении от 15 of September 2010 01:41:11 автор Sitsofe Wheeler написал:
> > > >     processor.max_cstate=2
> > > 
> > > Nope, it doesn't work with max_cstate=2
> > 
> > Perhaps intel_idle is being used? Any mention of it in dmesg?
> 
> Sitsofe, maybe you misunderstood me, I mean with max_cstate=1 graphics is
> smooth, with higher values (i.e. max_cstate=2) graphics is jerky.
> 
> Btw, Jesse, any comments/solutions/workarounds except one with
> processor.max_cstate=1 in kernel commandline? Should I file a bug on fdo
> bugzilla?

This looks like a problem I've seen on some hardware.

My workaround has been to use the pm_qos /dev/cpu_dma_latency interface to 
request a maximum latency of 1ms (value chosen as definitely small enough - a 
larger value may be better, but I don't care about power saving at runtime on 
my kit).

If it's happening on other kit, perhaps the i915 driver should make a suitable 
pm_qos request itself. Jesse, can you comment?
-- 
Simon Farnsworth
Software Engineer
ONELAN Limited
http://www.onelan.com/
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