[Intel-gfx] [PATCH igt] lib/gt: Insert an arbitration point in our hang batch

[Chris Wilson]

Quoting Chris Wilson (2017-10-27 13:59:17)
> Quoting Ville Syrjälä (2017-10-27 13:54:49)
> > On Fri, Oct 27, 2017 at 01:45:35PM +0100, Chris Wilson wrote:
> > > A purely recursive batch has the downside that it is a severe drain on
> > > system resources (see commit f978cc027cd0 "lib/dummyload: Pad with a few
> > > nops so that we do not completely hog the system") which can result in
> > > the test being starved and failing to make reasonably progress. For more
> > > reliable resets, also include an arbitration point. This should lessen
> > > the efficacy of the hang...
> > > 
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > > ---
> > >  lib/igt_gt.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/lib/igt_gt.c b/lib/igt_gt.c
> > > index 89727d22..2aebad14 100644
> > > --- a/lib/igt_gt.c
> > > +++ b/lib/igt_gt.c
> > > @@ -313,12 +313,12 @@ igt_hang_t igt_hang_ctx(int fd,
> > >       len = 2;
> > >       if (intel_gen(intel_get_drm_devid(fd)) >= 8)
> > >               len++;
> > > -     b[0] = MI_BATCH_BUFFER_START | (len - 2);
> > > -     b[len] = MI_BATCH_BUFFER_END;
> > > -     b[len+1] = MI_NOOP;
> > > -     gem_write(fd, exec.handle, 0, b, sizeof(b));
> > > +     b[0] = 0x5 << 24; /* ARB_CHk */
> > 
> > That seems to be gen4+ only. Also
> > "This instruction can be placed only in a ring buffer, never in a batch
> > buffer."
> 
> Idea of since/until when? It's definitely listed for batches on gen8+.
> 
> The good news being an unrecognised MI cmd it is skipped. Better news if
> it causes a GPU hang ;)

But it certainly doesn't work as an arbitration point on gen6, presuming
that was what we were missing for the reset to function.
-Chris