gallium: Add the ability to query a single pipeline statistics counter

Gallium historically has treated pipeline statistics queries as a single
query, PIPE_QUERY_PIPELINE_STATISTICS, which returns a block of 11
values.  This was originally patterned after the D3D1x API.  Much later,
Brian introduced an OpenGL extension that exposed these counters - but
it exposes 11 separate queries, each of which returns a single value.

Today, st/mesa simply queries all 11 values, and returns a single value.
While pipeline statistics counters aren't typically performance
critical, this is still not a great fit.  A D3D1x->GL translator might
request all 11 counters by creating 11 separate GL queries...which
Gallium would map to reads of all 11 values each time, resulting in a
total 121 counter reads.  That's not ideal.

This patch adds a new cap, PIPE_CAP_QUERY_PIPELINE_STATISTICS_SINGLE,
and corresponding query type PIPE_QUERY_PIPELINE_STATISTICS_SINGLE.
When calling create_query(), q->index should be set to one of the
PIPE_STAT_QUERY_* enums to select a counter.  Unlike the block query,
this returns the value in pipe_query_result::u64 (as it's a single
value) instead of the pipe_query_data_pipeline_statistics group.

We update st/mesa to expose ARB_pipeline_statistics_query if either
capability is set, preferring the new SINGLE variant when available.

Thanks to Roland, Ilia, and Marek for helping me sort this out.

Reviewed-by: Marek Olšák <[email protected]>
Reviewed-by: Tapani Pälli <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/gallium/include/pipe/p_defines.h b/src/gallium/include/pipe/p_defines.h
index 4480b54eb2f..d76fadadfdf 100644
--- a/src/gallium/include/pipe/p_defines.h
+++ b/src/gallium/include/pipe/p_defines.h
@@ -563,6 +563,7 @@ enum pipe_query_type {
    PIPE_QUERY_SO_OVERFLOW_ANY_PREDICATE,
    PIPE_QUERY_GPU_FINISHED,
    PIPE_QUERY_PIPELINE_STATISTICS,
+   PIPE_QUERY_PIPELINE_STATISTICS_SINGLE,
    PIPE_QUERY_TYPES,
    /* start of driver queries, see pipe_screen::get_driver_query_info */
    PIPE_QUERY_DRIVER_SPECIFIC = 256,
@@ -851,6 +852,7 @@ enum pipe_cap
    PIPE_CAP_MAX_VERTEX_ELEMENT_SRC_OFFSET,
    PIPE_CAP_SURFACE_SAMPLE_COUNT,
    PIPE_CAP_TGSI_ATOMFADD,
+   PIPE_CAP_QUERY_PIPELINE_STATISTICS_SINGLE,
 };
 
 /**