Looking at the distribution of i915_wait_request for a set of GL
benchmarks, we see:
broadwell# python bcc/tools/funclatency.py -u i915_wait_request
usecs : count distribution
0 -> 1 : 29184 |****************************************|
2 -> 3 : 5767 |******* |
4 -> 7 : 3000 |**** |
8 -> 15 : 491 | |
16 -> 31 : 140 | |
32 -> 63 : 203 | |
64 -> 127 : 543 | |
128 -> 255 : 881 |* |
256 -> 511 : 1209 |* |
512 -> 1023 : 1739 |** |
1024 -> 2047 : 22855 |******************************* |
2048 -> 4095 : 1725 |** |
4096 -> 8191 : 5813 |******* |
8192 -> 16383 : 5348 |******* |
16384 -> 32767 : 1000 |* |
32768 -> 65535 : 4400 |****** |
65536 -> 131071 : 296 | |
131072 -> 262143 : 225 | |
262144 -> 524287 : 4 | |
524288 -> 1048575 : 1 | |
1048576 -> 2097151 : 1 | |
2097152 -> 4194303 : 1 | |
broxton# python bcc/tools/funclatency.py -u i915_wait_request
usecs : count distribution
0 -> 1 : 5523 |************************************* |
2 -> 3 : 1340 |********* |
4 -> 7 : 2100 |************** |
8 -> 15 : 755 |***** |
16 -> 31 : 211 |* |
32 -> 63 : 53 | |
64 -> 127 : 71 | |
128 -> 255 : 113 | |
256 -> 511 : 262 |* |
512 -> 1023 : 358 |** |
1024 -> 2047 : 1105 |******* |
2048 -> 4095 : 848 |***** |
4096 -> 8191 : 1295 |******** |
8192 -> 16383 : 5894 |****************************************|
16384 -> 32767 : 4270 |**************************** |
32768 -> 65535 : 5622 |************************************** |
65536 -> 131071 : 306 |** |
131072 -> 262143 : 50 | |
262144 -> 524287 : 76 | |
524288 -> 1048575 : 34 | |
1048576 -> 2097151 : 0 | |
2097152 -> 4194303 : 1 | |
Picking 20us for the context-switch busyspin has the dual advantage of
catching most frequent short waits while avoiding the cost of a context
switch. 20us is a typical latency of 2 context-switches, i.e. the cost
of taking the sleep, without the secondary effects of cache flushing.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Sagar Kamble <sagar.a.kamble@xxxxxxxxx>
Cc: Eero Tamminen <eero.t.tamminen@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Ben Widawsky <ben@xxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
---
drivers/gpu/drm/i915/Kconfig.profile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/Kconfig.profile b/drivers/gpu/drm/i915/Kconfig.profile
index 63cb744d920d..de394dea4a14 100644
--- a/drivers/gpu/drm/i915/Kconfig.profile
+++ b/drivers/gpu/drm/i915/Kconfig.profile
@@ -14,7 +14,7 @@ config DRM_I915_SPIN_REQUEST_IRQ
config DRM_I915_SPIN_REQUEST_CS
int
- default 2 # microseconds
+ default 20 # microseconds
help
After sleeping for a request (GPU operation) to complete, we will
be woken up on the completion of every request prior to the one
--
2.18.0
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