[2.6.39-rc7] i915: kworker busily spinning...

[Daniel J Blueman]

On 24 May 2011 12:02, Andy Lutomirski <luto at mit.edu> wrote:
> On 05/17/2011 07:27 AM, Daniel J Blueman wrote:
>> With 2.6.39-rc7 on my Sandy Bridge laptop GPU (8086:0126 rev 9),
>> sometimes I find one of the kworker threads busily running with 15-20%
>> system time for some minutes, causing terrible interactivity latency.
>> I've seen it occur when plugging eg a HDMI display, and also when no
>> display has been plugged (ie only the internal LVDS connection is
>> active).
>>
>> Across multiple kernel task captures, I see the kernel thread
>> consistently reading one of the connector's EDID data [1]; I guess
>> either it's having a hard time reading from a disconnected connector
>> and retrying, or is incorrectly detecting a change when there is none.
>>
>> I'll enable DRM debugging to see what connectors it believes it needs
>> to read from. Anything else that would be handy to capture, or any
>> thoughts?
>>
>> Also, the 100ms connector change polling seems overkill, particularly
>> when power consumption is important; 1000-2000ms would be sufficient,
>> do you think?
>
> I think it's meant to be every 10 seconds.
>
> In any case, the output_poll_execute code does more work than necessary,
> which might exacerbate the problem.  Here's an old patch I wrote that
> probably doesn't apply any more but might help.

Thanks for the patch Andy; I'll test it after we've found a fix for
the underlying issue.

Daniel
-- 
Daniel J Blueman