[Intel-gfx] [PATCH v3 4/4] drm/i915: Improve long running OCL w/a for GuC submission
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Tue Mar 8 09:41:24 UTC 2022
On 03/03/2022 22:37, John.C.Harrison at Intel.com wrote:
> From: John Harrison <John.C.Harrison at 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.
>
> 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 at Intel.com>
> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com> (v1)
> Acked-by: Michal Mrozek <michal.mrozek at intel.com>
> ---
> 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 39328567c200..7cc38d25ee5c 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 4185c7338581..cc0954ad836a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -438,9 +438,14 @@ 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 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.
> + */
> 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;
I wouldn't go as far as adding a config option since as it is it only
applies to Gen12 but Kconfig text says nothing about that. And I am not
saying you should add a Gen12 specific config option, that would be
weird. So IMO just drop it.
Regards,
Tvrtko
>
> /* Cap properties according to any system limits */
> #define CLAMP_PROP(field) \
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