linux-kernel - responsiveness: newer kernels causing lagging and blocking

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Date:	Thu, 23 Feb 2012 17:30:41 +0100
From:	Stephan Bärwolf 
	<stephan.baerwolf@...ilmenau.de>
To:	linux-kernel@...r.kernel.org
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Buesch <mb@...sch.de>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Alex Deucher <alexdeucher@...il.com>,
	Dave Airlie <airlied@...hat.com>
Subject: responsiveness: newer kernels causing lagging and blocking

Under various conditions linux since 2.6.39-rc1 laggs and blocks enormously the whole system.
(For example while starting "winecfg" (on a thinkpad X220) and parallel moving the
mousecursor you can observe a periodic blocking for some seconds)

After bisecting a little while, commit "4819d2e4310796c4e9eef674499af9b9caf36b5a"
(" drm: Retry i2c transfer of EDID block after failure ") seems to be responsible.

Because function "drm_do_probe_ddc_edid" loops trying "i2c_transfer" it consumes a lot
of time during errors. Reverting or changing "retries" from 5 to 1 extremly minimizes the
problem to "not perceptible".
It seems the locking within "i2c_transfer" slows everything down.
So maybe it is possible to yield() before calling it?

regards Stephan
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