[Intel-gfx] i915 irq storm mitigation in 3.10

[Daniel Vetter]

On Sun, Jul 21, 2013 at 10:23 PM, Jan Niggemann <jn at hz6.de> wrote:
>> 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.

Hm, that sounds like something doesn't quite work as expected. We
should kill things once we get 5 interrupts or so in 1 second. So if
it's bad enough that it slows your machine down it really should only
be barely noticeable.

Can you please boot with drm.debug=0xe added to your kernel cmdline,
do a cold boot (so that we get a storm) and then once everything is
quiet grab the full kernel log (you probably have to grab it from the
disk, dmesg has likely overflown) and upload it somewhere (since it's
probably too big for the mailing lists)? Please also enable printk
timestamps for your kernel so that we can create a timeline of
everything going on.

That log should give us a starting point, but I guess we need to run
some debug patches past you to figure out what's going on in your
system exactly.

> 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...

We'll only enable ports (and interrupts for them) if we think they're
there. Could it be that there's a docking station for your machine
available which would have these ports?

> 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.

That's not good, we need to fix this. Also adding Egbert, maybe he has
seen something like this in the wild already, after all he's
implemented the storm handling code.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch