From: John Harrison John.C.Harrison@Intel.com
A workaround was added to the driver to allow OpenCL 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 OpenCL 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 OpenCL can have long running threads.
So, rather than disabling the timeout completely, just set it to a 'long' value.
CC: Michal Mrozek michal.mrozek@intel.com Signed-off-by: John Harrison John.C.Harrison@Intel.com Reviewed-by: Daniele Ceraolo Spurio daniele.ceraolospurio@intel.com --- drivers/gpu/drm/i915/gt/intel_engine_cs.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c index 2a1e9f36e6f5..64249301a227 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c @@ -385,9 +385,25 @@ 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. */ - if (GRAPHICS_VER(i915) == 12 && engine->class == RENDER_CLASS) - engine->props.preempt_timeout_ms = 0; + /* + * Mid-thread pre-emption is not available in Gen12. Unfortunately, + * some OpenCL 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. + * Using three times the heartbeat period seems long enough for a + * reasonable task to reach a pre-emption point but not so long as to + * allow genuine hangs to go unresolved. + */ + if (GRAPHICS_VER(i915) == 12 && engine->class == RENDER_CLASS) { + unsigned long triple_beat = engine->props.heartbeat_interval_ms * 3; + + if (triple_beat > engine->props.preempt_timeout_ms) { + drm_info(>->i915->drm, "Bumping pre-emption timeout from %ld to %ld on %s to allow slow compute pre-emption\n", + engine->props.preempt_timeout_ms, triple_beat, engine->name); + + engine->props.preempt_timeout_ms = triple_beat; + } + }
/* Cap timeouts to prevent overflow inside GuC */ if (intel_guc_submission_is_wanted(>->uc.guc)) {