[Intel-gfx] [PATCH] drm/i915: Allow userspace to request no-error-capture upon GPU hangs

[Daniel Vetter]

On Wed, Dec 16, 2015 at 10:00:44AM +0000, Chris Wilson wrote:
> On Wed, Dec 16, 2015 at 09:54:47AM +0100, Daniel Vetter wrote:
> > On Fri, Dec 11, 2015 at 10:18:35PM +0000, Chris Wilson wrote:
> > > igt likes to inject GPU hangs into its command streams. However, as we
> > > expect these hangs, we don't actually want them recorded in the dmesg
> > > output or stored in the i915_error_state (usually). To accomodate this
> > > allow userspace to set a flag on the context that any hang emanating
> > > from that context will not be recorded. We still do the error capture
> > > (otherwise how do we find the guilty context and know its intent?) as
> > > part of the reason for random GPU hang injection is to exercise the race
> > > conditions between the error capture and normal execution.
> > > 
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > 
> > Hm, I do like that we exercise the full paths all the time, increasing
> > chances for fireworks. What's the motivation here? Is there some
> > substantial speed-up?
> 
> No, since we keep doing the error-capture (we have to, we haven't fixed
> the bugs in it yet!), the only benefits are:
> 
> (a) Reduce dmesg spam during igt
> (b) simulating hangs doesn't leave an error-state around, or rather, we
> don't leave the simulated error state and igt doesn't eat a *genuine* hang
> that occurred during or before the test.

Oh, should better wait for coffee to kick in - I didn't realize that all
that code still runs, and the only thing that changes is whether we'll
store the capture error state in the global slot used by debugfs.

Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch