[Mesa-dev] [PATCH] i965: perf: minimize the chances to spread queries across batchbuffers

[Lionel Landwerlin]

On 24/07/17 16:55, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2017-06-22 02:25:28)
>> 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 at intel.com>
>> ---
>>   src/mesa/drivers/dri/i965/brw_performance_query.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_performance_query.c b/src/mesa/drivers/dri/i965/brw_performance_query.c
>> index 06576a54d03..6b874d0bbee 100644
>> --- a/src/mesa/drivers/dri/i965/brw_performance_query.c
>> +++ b/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);
> Doesn't this make more sense before the start of the perf-query, because
> you want the bookkends in the same batch? Flushing afterwards does
> nothing to improve the likelihood of this query being contained.

Indeed having it after might produce a spike in the first query.

Will send a follow up fix (and verify spikes are still gone).
Tough we'll still need this commit in stable before the following.

Thanks!

>
>>         --brw->perfquery.n_active_oa_queries;
>>   
>>         /* NB: even though the query has now ended, it can't be accumulated
>> -- 
>> 2.11.0
>>
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