Re: [PATCH v2] drm/i915: Reduce context HW ID lifetime

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Tvrtko Ursulin (2018-09-05 10:49:02)
> 
> On 04/09/2018 16:31, Chris Wilson wrote:
> > Future gen reduce the number of bits we will have available to
> > differentiate between contexts, so reduce the lifetime of the ID
> > assignment from that of the context to its current active cycle (i.e.
> > only while it is pinned for use by the HW, will it have a constant ID).
> > This means that instead of a max of 2k allocated contexts (worst case
> > before fun with bit twiddling), we instead have a limit of 2k in flight
> > contexts (minus a few that have been pinned by the kernel or by perf).
> > 
> > To reduce the number of contexts id we require, we allocate a context id
> > on first and mark it as pinned for as long as the GEM context itself is,
> > that is we keep it pinned it while active on each engine. If we exhaust
> > our context id space, then we try to reclaim an id from an idle context.
> > In the extreme case where all context ids are pinned by active contexts,
> > we force the system to idle in order to recover ids.
> > 
> > We cannot reduce the scope of an HW-ID to an engine (allowing the same
> > gem_context to have different ids on each engine) as in the future we
> > will need to preassign an id before we know which engine the
> > context is being executed on.
> > 
> > v2: Improved commentary (Tvrtko) [I tried at least]
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=107788
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> > Cc: Michel Thierry <michel.thierry@intel.com>
> > Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
[snip]
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Pushed, thanks for the review. I hope the silence is because it just
works and you guys foresee no problems with guc/hw integration! :)
-Chris
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