[igt-dev] [PATCH igt] igt/gem_ctx_isolation: Reset a scratch context

[Chris Wilson]

Quoting Chris Wilson (2018-03-27 14:52:20)
> Quoting Chris Wilson (2018-03-27 14:48:43)
> > If we inject a reset into the target context, there is a risk that the
> > register state is never saved back to memory. The exact interaction
> > between reset, the context image and the precise timing of our execution
> > are not well defined. Since we cannot ensure that the context image
> > remains valid, force a context switch prior to the reset.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105270
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105457
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105545
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > ---
> >  tests/gem_ctx_isolation.c | 28 +++++++++++++++++++++++++++-
> >  1 file changed, 27 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tests/gem_ctx_isolation.c b/tests/gem_ctx_isolation.c
> > index d8109aa0..4968e367 100644
> > --- a/tests/gem_ctx_isolation.c
> > +++ b/tests/gem_ctx_isolation.c
> > @@ -522,6 +522,32 @@ static void isolation(int fd,
> >  #define S4 (4 << 8)
> >  #define SLEEP_MASK (0xf << 8)
> >  
> > +static void inject_reset_context(int fd, unsigned int engine)
> > +{
> > +       igt_spin_t *spin;
> > +       uint32_t ctx;
> > +
> > +       /*
> > +        * Force a context switch before triggering the reset, or else
> > +        * we risk corrupting the target context and we can't blame the
> > +        * HW for screwing up if the context was already broken.
> > +        */
> > +
> > +       ctx = gem_context_create(fd);
> > +       if (gem_can_store_dword(fd, engine)) {
> > +               spin = __igt_spin_batch_new_poll(fd, ctx, engine);
> > +               igt_spin_busywait_until_running(spin);
> > +       } else {
> > +               spin = __igt_spin_batch_new(fd, ctx, engine, 0);
> > +               usleep(1000); /* better than nothing */
> > +       }
> 
> Tvrtko, maybe we want igt_spin_batch_run()? Not sure though, so far we
> have an example where you need precise control and a couple of examples
> where we just want a running spinner.

Also this whole function might want to make its way into lib/i915 as the
basis of all hang/reset injection. Some improvement required to set
context parameters (e.g. disabling error state capturing) and skipping
if no reset is available or disabled (although that's the job for the
fixture, so may not be required for the library function). I'm sure
someone will catch me reusing this chunk over and over again...
-Chris