i965/query: Cache whether the batch references the query BO.

i965/query: Cache whether the batch references the query BO.

Chris Wilson noted that repeated calls to CheckQuery() would call
drm_intel_bo_references(brw->batch.bo, query->bo) on each invocation,
which is expensive.  Once we've flushed, we know that future batches
won't reference query->bo, so there's no point in asking more than once.

This patch adds a brw_query_object::flushed flag, which is a
conservative estimate of whether the batch has been flushed.

On the first call to CheckQuery() or WaitQuery(), we check if the
batch references query->bo.  If not, it must have been flushed for
some reason (such as being full).  We record that it was flushed.
If it does reference query->bo, we explicitly flush, and record that
we did so.

Any subsequent checks will simply see that query->flushed is set,
and skip the drm_intel_bo_references() call.

Inspired by a patch from Chris Wilson.

According to Eero, this does not affect the performance of Witcher 2
on Haswell, but approximately halves the userspace CPU usage.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86969
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>