Commit d7a8680e authored by John Harrison's avatar John Harrison
Browse files

drm/i915: Improve long running compute w/a for GuC submission 



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: default avatarJohn Harrison <John.C.Harrison@Intel.com>
Reviewed-by: default avatarDaniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Acked-by: default avatarMichal Mrozek <michal.mrozek@intel.com>
Acked-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221006213813.1563435-5-John.C.Harrison@Intel.com
parent 47daf84a

drivers/gpu/drm/i915/Kconfig.profile

+22 −4
Original line number Diff line number Diff line
@@ -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

drivers/gpu/drm/i915/gt/intel_engine_cs.c

+7 −2
Original line number Diff line number Diff line
@@ -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) \