[Mesa-dev] [PATCH 5/6] i965: Always flush caches after blitting to a GL buffer object.

Kenneth Graunke kenneth at whitecape.org
Tue Aug 29 21:28:42 UTC 2017

When we blit data into a buffer object, we may need to invalidate any
caches that might contain stale data, so the new data becomes visible.

For example, if the buffer object is bound as a vertex buffer, we need
to invalidate the vertex fetch cache.

While this flushing was missing, it usually happened implicitly for
non-obvious reasons: we're usually on the render ring, and calling
intel_emit_linear_blit() would require switching to the BLT ring,
causing an implicit flush.  This likely provoked the kernel to do
PIPE_CONTROLs on our behalf.  Although, Gen4-5 wouldn't have this
behavior.  At any rate, we should do it ourselves.
 src/mesa/drivers/dri/i965/intel_buffer_objects.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/intel_buffer_objects.c b/src/mesa/drivers/dri/i965/intel_buffer_objects.c
index dd6fca12d0b..01443c2b7fc 100644
--- a/src/mesa/drivers/dri/i965/intel_buffer_objects.c
+++ b/src/mesa/drivers/dri/i965/intel_buffer_objects.c
@@ -298,6 +298,7 @@ brw_buffer_subdata(struct gl_context *ctx,
                                 intel_obj->buffer, offset,
                                 temp_bo, 0,
+         brw_emit_mi_flush(brw);
          mark_buffer_valid_data(intel_obj, offset, size);
@@ -541,6 +542,7 @@ brw_flush_mapped_buffer_range(struct gl_context *ctx,
                          obj->Mappings[index].Offset + offset,
+   brw_emit_mi_flush(brw);
@@ -570,6 +572,7 @@ brw_unmap_buffer(struct gl_context *ctx,
          mark_buffer_gpu_usage(intel_obj, obj->Mappings[index].Offset,
+         brw_emit_mi_flush(brw);
       /* Since we've emitted some blits to buffers that will (likely) be used
@@ -577,7 +580,6 @@ brw_unmap_buffer(struct gl_context *ctx,
        * flush.  Once again, we wish for a domain tracker in libdrm to cover
        * usage inside of a batchbuffer.
-      brw_emit_mi_flush(brw);
       intel_obj->range_map_bo[index] = NULL;

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