Mesa (master): i965: fix cycle estimates when there's a pipeline stall
Connor Abbott
cwabbott0 at kemper.freedesktop.org
Fri Oct 30 06:20:14 UTC 2015
Module: Mesa
Branch: master
Commit: 6f231fddff1661c2ca2cfb7bb7a0e6a970bcbf40
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=6f231fddff1661c2ca2cfb7bb7a0e6a970bcbf40
Author: Connor Abbott <cwabbott0 at gmail.com>
Date: Fri Jun 5 19:20:57 2015 -0400
i965: fix cycle estimates when there's a pipeline stall
The issue time for an instruction is how many cycles it takes to
actually put it into the pipeline. If there's a pipeline stall that
causes the instruction to be delayed, we should first take that into
account to figure out when the instruction would start executing and
*then* add the issue time. The old code had it backwards, and so we
would underestimate the total time whenever we thought there would be a
pipeline stall by up to the issue time of the instruction.
Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>
---
src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
index cd1f21e..3e86cb0 100644
--- a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
+++ b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
@@ -1405,18 +1405,19 @@ instruction_scheduler::schedule_instructions(bblock_t *block)
instructions_to_schedule--;
update_register_pressure(chosen->inst);
+ /* If we expected a delay for scheduling, then bump the clock to reflect
+ * that. In reality, the hardware will switch to another hyperthread
+ * and may not return to dispatching our thread for a while even after
+ * we're unblocked. After this, we have the time when the chosen
+ * instruction will start executing.
+ */
+ time = MAX2(time, chosen->unblocked_time);
+
/* Update the clock for how soon an instruction could start after the
* chosen one.
*/
time += issue_time(chosen->inst);
- /* If we expected a delay for scheduling, then bump the clock to reflect
- * that as well. In reality, the hardware will switch to another
- * hyperthread and may not return to dispatching our thread for a while
- * even after we're unblocked.
- */
- time = MAX2(time, chosen->unblocked_time);
-
if (debug) {
fprintf(stderr, "clock %4d, scheduled: ", time);
bs->dump_instruction(chosen->inst);
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