[Intel-gfx] [PATCH 4/4] drm/i915: Improve long running OCL w/a for GuC submission

John.C.Harrison
2021-12-11T06:59:19Z

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. Likewise, bump the heartbeat interval. That gives the
OpenCL thread sufficient time to reach a pre-emption point without
being killed off either by the GuC or by the heartbeat.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
---
drivers/gpu/drm/i915/gt/intel_engine_cs.c | 42 +++++++++++++++++++++--
1 file changed, 39 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 352254e001b4..26af8d60fe2b 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -382,9 +382,45 @@ 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.
+ * The execlist solution was to disable pre-emption completely.
+ * However, pre-emption timeouts are the way GuC detects hung contexts
+ * and triggers engine resets. Thus, without pre-emption, there is no
+ * per engine reset. And full GT reset is much more intrusive. So keep
+ * the timeout for GuC submission platforms and just bump it to be
+ * much larger. Also bump the heartbeat timeout to match, otherwise
+ * the heartbeat can expire before the pre-emption can timeout and
+ * thus trigger a full GT reset anyway.
+ */
+ if (GRAPHICS_VER(i915) == 12 && engine->class == RENDER_CLASS) {
+ if (intel_uc_wants_guc_submission(&gt->uc)) {
+ const unsigned long min_preempt = 7500;
+ const unsigned long min_beat = 5000;
+
+ if (engine->props.preempt_timeout_ms &&
+ engine->props.preempt_timeout_ms < min_preempt) {
+ drm_info(&gt->i915->drm, "Bumping pre-emption timeout from %ld to %ld on %s to allow slow compute pre-emption\n",
+ engine->props.preempt_timeout_ms,
+ min_preempt, engine->name);
+
+ engine->props.preempt_timeout_ms = min_preempt;
+ }
+
+ if (engine->props.heartbeat_interval_ms &&
+ engine->props.heartbeat_interval_ms < min_beat) {
+ drm_info(&gt->i915->drm, "Bumping heartbeat interval from %ld to %ld on %s to allow slow compute pre-emption\n",
+ engine->props.heartbeat_interval_ms,
+ min_beat, engine->name);
+
+ engine->props.heartbeat_interval_ms = min_beat;
+ }
+ } else {
+ engine->props.preempt_timeout_ms = 0;
+ }
+ }

engine->defaults = engine->props; /* never to change again */

--
2.25.1