[Mesa-dev] [PATCH 09/10] i965/vs: Use write commits on scratch writes in pre-gen6.
Eric Anholt
eric at anholt.net
Fri Sep 2 18:37:19 PDT 2011
This is required to ensure ordering between reads and writes within a
thread.
---
src/mesa/drivers/dri/i965/brw_vec4_emit.cpp | 24 ++++++++++++++++++++++--
1 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
index ac1ef0d..30bb0f6 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
@@ -431,6 +431,7 @@ vec4_visitor::generate_scratch_write(vec4_instruction *inst,
struct brw_reg index)
{
struct brw_reg header = brw_vec8_grf(0, 0);
+ bool write_commit;
/* If the instruction is predicated, we'll predicate the send, not
* the header setup.
@@ -455,6 +456,25 @@ vec4_visitor::generate_scratch_write(vec4_instruction *inst,
brw_set_predicate_control(p, inst->predicate);
+ /* Pre-gen6, we have to specify write commits to ensure ordering
+ * between reads and writes within a thread. Afterwards, that's
+ * guaranteed and write commits only matter for inter-thread
+ * synchronization.
+ */
+ if (intel->gen >= 6) {
+ write_commit = false;
+ } else {
+ /* The visitor set up our destination register to be g0. This
+ * means that when the next read comes along, we will end up
+ * reading from g0 and causing a block on the write commit. For
+ * write-after-read, we are relying on the value of the previous
+ * read being used (and thus blocking on completion) before our
+ * write is executed. This means we have to be careful in
+ * instruction scheduling to not violate this assumption.
+ */
+ write_commit = true;
+ }
+
/* Each of the 8 channel enables is considered for whether each
* dword is written.
*/
@@ -470,9 +490,9 @@ vec4_visitor::generate_scratch_write(vec4_instruction *inst,
3, /* mlen */
true, /* header present */
false, /* pixel scoreboard */
- 0, /* rlen */
+ write_commit, /* rlen */
false, /* eot */
- false /* commit */);
+ write_commit);
}
void
--
1.7.5.4
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