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    • Chris Wilson's avatar
      drm/i915: Track number of pending freed objects · c9c70471
      Chris Wilson authored
      
      
      During igt, we frequently call into the driver to reset both HW and
      driver state (idling the device, waiting for it to become idle and
      freeing off old objects) to ensure that we start each test/subtest/pass
      from known state. This process incurs an RCU barrier or two to ensure
      that any such pending frees are indeed flushed before we return.
      However, unconditionally waiting on the RCU barrier adds needless delay
      to many callers, which adds up to several seconds when repeated thousands
      of times. We can skip the rcu_barrier() if by tracking how many outstanding
      frees we have, we know there are none.
      
      The same path is used along suspend, where we may be able to save the
      unconditional RCU barrier.
      
      To put it into perspective with a completely meaningless
      microbenchmark, igt/gem_sync/idle is improved from 50ms to 30us on bdw.
      
      v2: Remove the extra synchronize_rcu() inside i915_drop_caches_set()
      
      Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
      Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
      Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
      Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
      Link: https://patchwork.freedesktop.org/patch/msgid/20180219220631.25001-1-chris@chris-wilson.co.uk
      c9c70471