i965: perf: minimize the chances to spread queries across batchbuffers

Counter related to timings will be sensitive to any delay introduced
by the software. In particular if our begin & end of performance
queries end up in different batches, time related counters will
exhibit biffer values caused by the time it takes for the kernel
driver to load new requests into the hardware.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_performance_query.c

@@ -1063,6 +1063,14 @@ brw_end_perf_query(struct gl_context *ctx,
                                              obj->oa.begin_report_id + 1);
       }
 
+      /* We flush the batchbuffer here to minimize the chances that MI_RPC
+       * delimiting commands end up in different batchbuffers. If that's the
+       * case, the measurement will include the time it takes for the kernel
+       * scheduler to load a new request into the hardware. This is manifested
+       * in tools like frameretrace by spikes in the "GPU Core Clocks"
+       * counter.
+       */
+      intel_batchbuffer_flush(brw);
       --brw->perfquery.n_active_oa_queries;
 
       /* NB: even though the query has now ended, it can't be accumulated