drm/i915: Replace global bsd_dispatch_index with random seed

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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!) Removing the global is one less variable we have to find a home
for!

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

No user is advised to use this method; the current suggestion is to use
a virtual engine for agnostic batches, randomised submission or using
the busyness tracking to select the most idle engine at the time of
dispatch. 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@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190809091010.23281-2-chris@chris-wilson.co.uk

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This commit is contained in:

Chris Wilson 2019-08-09 10:10:09 +01:00

parent d5b2a3a4f8

commit 6b86f90019

3 changed files with 1 additions and 7 deletions

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3

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

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3

drivers/gpu/drm/i915/i915_drv.h

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2

drivers/gpu/drm/i915/i915_gem.c

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