linux-kernel - Re: Intel graphics CPU usage

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Message-ID: <20100816025146.GA1639@arch.tripp.de>
Date:	Mon, 16 Aug 2010 04:51:46 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Airlie <airlied@...ux.ie>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Zhao Yakui <yakui.zhao@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Adam Jackson <ajax@...hat.com>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Intel graphics CPU usage - SDVO detect bogosity?

On Sun, Aug 15, 2010 at 07:32:15PM -0700, Linus Torvalds wrote:
> I started wondering why 'top' was showing an otherwise idle system as
> having a load average of 0.5+, and worker threads constantly using the
> CPU.
> 
> So I did a system-wide profile, and got the attached output (look at
> it in a really wide terminal).
> 
> There seems to be something _seriously_ wrong with i915 SDVO detect.
> This is on an Apple Mac Mini (hey, your favorite problem child!), and
> apparently it spends 20% of its non-idle CPU time just doing udelay's
> for the i2c SDVO connection detection.
> 
> That sounds a bit wrong, doesn't it?
> 
> I don't know how recent this is - it might have been going on for some
> time without me noticing. It's the wife's computer, and the same thing
> doesn't seem to happen on my Core i5 desktop
> 
> Any ideas? Any information I can give about the machine?

You're not alone. I'm seeing similar things on my machine (AMD,Radeon).
The monitor outputs are polled every 10 sec in drivers/gpu/drm/drm_crtc_helper.c.

There is a patch attached to the following bug report that disables
polling and solves the problem for me:
http://bugs.freedesktop.org/show_bug.cgi?id=29536

-- 
»A man who doesn't know he is in prison can never escape.«
William S. Burroughs
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