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) \
