[igt-dev] [PATCH i-g-t] tests/kms_concurrent: For i915 devices run allocator in multiprocess mode

[Petri Latvala]

On Fri, May 20, 2022 at 09:11:18AM +0200, Zbigniew Kempczyński wrote:
> On Fri, May 20, 2022 at 08:56:29AM +0300, Petri Latvala wrote:
> > On Thu, May 19, 2022 at 04:17:45PM +0200, Zbigniew Kempczyński wrote:
> > > Test calls igt_fork() so for i915 requires offset allocation arbitration
> > > (allocator in multiprocess mode) especially when same drm fd is used
> > > in children. Dedicated thread (intel_allocator_multiprocess_start())
> > > is required to be started on the very beginning to handle offset
> > > allocations as well as stopping it (intel_allocator_multiprocess_stop())
> > > before test exits.
> > > 
> > > Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> > > Cc: Luciano Coelho <luciano.coelho at intel.com>
> > > Cc: Swati Sharma <swati2.sharma at intel.com>
> > 
> > Acked-by: Petri Latvala <petri.latvala at intel.com>
> > 
> > Now, having said that:
> > 
> > The test itself doesn't touch the allocator at all, it's done by
> > igt_fb.c's blitcopy() under the hood. Did you check if there's any
> > other tests that could have this problem? Suggesting a common way to
> > have tests communicate their intention to fork is overkill at this
> > point, unless the problem is widespread.
> 
> Take a look to kms_busy.c function flip_to_fb.c. There's igt_fork()
> but we don't need to run additional allocator thread. 
> 
> I think we can try:
> 1. run multiprocess allocator thread on all igt run but this is imo
>    overkill, especially if test works on separate vm's it can "detach"
>    and become standalone allocator,
> 2. add some debug information instead of segfaulting that multiprocess
>    allocator is likely required in the test. IGT already got similar
>    code (like internal_assert in igt_describe_f()).

Debug information sounds really good. It's easy to detect the crashing
case in the allocator code after all, from what I remember about the
backtrace.


-- 
Petri Latvala