On 28/07/2018 17:46, Chris Wilson wrote:
Looking at the distribution of i915_wait_request for a set of GL
What was the set?
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 <[email protected]> Cc: Sagar Kamble <[email protected]> Cc: Eero Tamminen <[email protected]> Cc: Tvrtko Ursulin <[email protected]> Cc: Ben Widawsky <[email protected]> Cc: Joonas Lahtinen <[email protected]> Cc: Michał Winiarski <[email protected]> --- 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_IRQconfig DRM_I915_SPIN_REQUEST_CSint - 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
I'd be more tempted to pick 10us given the histograms. It would avoid wasting cycles on Broadwell and keep the majority of the benefit on Broxton.
However.. it also raises the question if we perhaps want to have this initialized per-platform at runtime.. ? That would open up the way of auto-tuning it, if the goal is to eliminate the low part of the histogram.
Also, please add to the commit what kind of perf/watt or something effect on the benchmarks we get with it.
Regards, Tvrtko _______________________________________________ Intel-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/intel-gfx
