[Intel-gfx] i915 irq storm mitigation in 3.10

[Jan Niggemann]

Hi list,

I was busy, but this is important so I report my findings:

Am 08.07.2013 22:03, schrieb Daniel Vetter:
> On Sat, Jul 06, 2013 at 11:41:07PM +0200, Jan Niggemann wrote:
>> Hi list,
>>
>> I'm not sure, but I think the recent patch to keep i915 systems from
>> locking up / slowing down in case of irq storms didn't fully help.
>> I compiled 3.10, but every now and then, my system has the same
>> symptoms as before.
>>
>> grep storm /var/log/messages
>> Jul  5 21:55:43 muretop kernel: [  324.767375] [drm] HPD interrupt
>> storm detected on connector DP-3: switching from hotplug detection
>> to polling
>> Jul  6 23:05:57 muretop kernel: [  200.372208] [drm] HPD interrupt
>> storm detected on connector HDMI-A-1: switching from hotplug
>> detection to polling
>> Jul  6 23:07:51 muretop kernel: [  313.752039] [drm] HPD interrupt
>> storm detected on connector DP-3: switching from hotplug detection
>> to pol
>>
>> I notice up to 50% CPU from kworker/u8:0 when my system slows down.
>>
>> I'm new to kernel development, but if you tell me what to do, I'm
>> very willing to help diagnosing this.
>
> Seems to work as advertised, once we detect a storm we kill the 
> hotplug
> interrupt. Note that since on many systems these storms only happen 
> in
> certain conditions (e.g. specific battery charger state) we'll 
> re-enable
> the interrupts every 2 minutes to check whether the storm has passed
> (there's not really any other way).
OK, I didn't know it worked that way.

> But every time this happens we only let through a few interrupts, so 
> this
> shouldn't affect you badly. Can you please check whether those 
> slowdowns
> line up with 2 minute intervalls?
I observed these slowdowns for a couple of weeks now. On my machine, 
they only happen once, some minutes after a cold boot.
They last for a minute or two, and then they are gone.
I'd have guessed that the storm detection kicks in pretty quickly after 
a storm is detected and that it would go unnoticed.

Another thing I have noticed: All storm-related messages are about DP-3 
and HDMI-A-1, but my T400 doesn't have either a HDMI out nor a 
DisplayPort connector...

I returned to 3.2.0 with drm_kms_helper.poll=0 for the time being, so 
this doesn't affect me badly.
Please tell me if and how I can further diagnose this.

Jan