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

[Chris Wilson]

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.

>        --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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