[Intel-gfx] i915 irq storm mitigation in 3.10

[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).

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?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch