[Intel-gfx] [PATCH] drm/i915: Replace global bsd_dispatch_index with random seed

[Chris Wilson]

Quoting Joonas Lahtinen (2019-08-09 09:04:56)
> Quoting Chris Wilson (2019-08-08 12:27:48)
> > We keep a global seed for the legacy BSD round-robin selector, but in
> > our testing of multiple simultaneous client workloads, a random seed
> > spreads the load more evenly. (As even as an initial round-robin selector
> > can be!)
> 
> A sentence could be added about the test scenario.

We can simulate multi-client (both same and mixed workloads) using
gem_wsim to work out optimal strategies and then compare our simulation
with the actual transcoder. This fixed round-robin turns out to be one
of the worst.

No user is advised to use this method. At the present time, intel-media
is explicit, but libva still seems to use it, with the exception of
batches that must execute on vcs0. Oh well.

> > 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>
> 
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> 
> Regards, Joonas
>