Re: [PATCH v4 4/4] drm/i915: Improve long running compute w/a for GuC submission

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On 29/09/2022 03:18, John.C.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>

A workaround was added to the driver to allow compute workloads to run
'forever' by disabling pre-emption on the RCS engine for Gen12.
It is not totally unbound as the heartbeat will kick in eventually
and cause a reset of the hung engine.

However, this does not work well in GuC submission mode. In GuC mode,
the pre-emption timeout is how GuC detects hung contexts and triggers
a per engine reset. Thus, disabling the timeout means also losing all
per engine reset ability. A full GT reset will still occur when the
heartbeat finally expires, but that is a much more destructive and
undesirable mechanism.

The purpose of the workaround is actually to give compute tasks longer
to reach a pre-emption point after a pre-emption request has been
issued. This is necessary because Gen12 does not support mid-thread
pre-emption and compute tasks can have long running threads.

So, rather than disabling the timeout completely, just set it to a
'long' value.

v2: Review feedback from Tvrtko - must hard code the 'long' value
instead of determining it algorithmically. So make it an extra CONFIG
definition. Also, remove the execlist centric comment from the
existing pre-emption timeout CONFIG option given that it applies to
more than just execlists.

Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx> (v1)
Acked-by: Michal Mrozek <michal.mrozek@xxxxxxxxx>

Acked-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko

---
  drivers/gpu/drm/i915/Kconfig.profile      | 26 +++++++++++++++++++----
  drivers/gpu/drm/i915/gt/intel_engine_cs.c |  9 ++++++--
  2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/Kconfig.profile b/drivers/gpu/drm/i915/Kconfig.profile
index 39328567c2007..7cc38d25ee5c8 100644
--- a/drivers/gpu/drm/i915/Kconfig.profile
+++ b/drivers/gpu/drm/i915/Kconfig.profile
@@ -57,10 +57,28 @@ config DRM_I915_PREEMPT_TIMEOUT
  	default 640 # milliseconds
  	help
  	  How long to wait (in milliseconds) for a preemption event to occur
-	  when submitting a new context via execlists. If the current context
-	  does not hit an arbitration point and yield to HW before the timer
-	  expires, the HW will be reset to allow the more important context
-	  to execute.
+	  when submitting a new context. If the current context does not hit
+	  an arbitration point and yield to HW before the timer expires, the
+	  HW will be reset to allow the more important context to execute.
+
+	  This is adjustable via
+	  /sys/class/drm/card?/engine/*/preempt_timeout_ms
+
+	  May be 0 to disable the timeout.
+
+	  The compiled in default may get overridden at driver probe time on
+	  certain platforms and certain engines which will be reflected in the
+	  sysfs control.
+
+config DRM_I915_PREEMPT_TIMEOUT_COMPUTE
+	int "Preempt timeout for compute engines (ms, jiffy granularity)"
+	default 7500 # milliseconds
+	help
+	  How long to wait (in milliseconds) for a preemption event to occur
+	  when submitting a new context to a compute capable engine. If the
+	  current context does not hit an arbitration point and yield to HW
+	  before the timer expires, the HW will be reset to allow the more
+	  important context to execute.
This is adjustable via
  	  /sys/class/drm/card?/engine/*/preempt_timeout_ms
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index fcbccd8d244e9..c1257723d1949 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -508,9 +508,14 @@ static int intel_engine_setup(struct intel_gt *gt, enum intel_engine_id id,
  	engine->props.timeslice_duration_ms =
  		CONFIG_DRM_I915_TIMESLICE_DURATION;
- /* Override to uninterruptible for OpenCL workloads. */
+	/*
+	 * Mid-thread pre-emption is not available in Gen12. Unfortunately,
+	 * some compute workloads run quite long threads. That means they get
+	 * reset due to not pre-empting in a timely manner. So, bump the
+	 * pre-emption timeout value to be much higher for compute engines.
+	 */
  	if (GRAPHICS_VER(i915) == 12 && (engine->flags & I915_ENGINE_HAS_RCS_REG_STATE))
-		engine->props.preempt_timeout_ms = 0;
+		engine->props.preempt_timeout_ms = CONFIG_DRM_I915_PREEMPT_TIMEOUT_COMPUTE;
/* Cap properties according to any system limits */
  #define CLAMP_PROP(field) \



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