[Intel-gfx] [28/33] drm/i915/gt: Expose timeslice duration to sysfs

[Steve Carbonari]

On Thu, Dec 12, 2019 at 02:04:54PM +0000, Chris Wilson wrote:
> Execlists uses a scheduling quantum (a timeslice) to alternate execution
> between ready-to-run contexts of equal priority. This ensures that all
> users (though only if they of equal importance) have the opportunity to
> run and prevents livelocks where contexts may have implicit ordering due
> to userspace semaphores.
> 
> The timeslicing mechanism can be compiled out with
> 
> 	./scripts/config --set-val DRM_I915_TIMESLICE_DURATION 0
> 
> The timeslice duration can be adjusted per-engine using,
> 
> 	/sys/class/drm/card?/engine/*/timeslice_duration_ms
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Code looks good.
Tested the patch with previous patches in the series.
[26/33] drm/i915/gt: Expose engine properties via sysfs
[27/33] drm/i915/gt: Expose engine->mmio_base via sysfs
The directories and files show up with expected values.
Verified that if engine does not have timeslices the
sysfs entry is not created.

Reviewed-by: Steve Carbonari <steven.carbonari at intel.com>
Tested-by: Steve Carbonari <steven.carbonari at intel.com


> ---
>  drivers/gpu/drm/i915/Kconfig.profile         |  3 ++
>  drivers/gpu/drm/i915/gt/intel_engine_sysfs.c | 46 ++++++++++++++++++++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig.profile b/drivers/gpu/drm/i915/Kconfig.profile
> index c280b6ae38eb..d8d4a16179bd 100644
> --- a/drivers/gpu/drm/i915/Kconfig.profile
> +++ b/drivers/gpu/drm/i915/Kconfig.profile
> @@ -73,4 +73,7 @@ config DRM_I915_TIMESLICE_DURATION
>  	  is scheduled for execution for the timeslice duration, before
>  	  switching to the next context.
>  
> +	  This is adjustable via
> +	  /sys/class/drm/card?/engine/*/timeslice_duration_ms
> +
>  	  May be 0 to disable timeslicing.
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_sysfs.c b/drivers/gpu/drm/i915/gt/intel_engine_sysfs.c
> index abddd8d0f9ae..b1bd768b13d7 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_sysfs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_sysfs.c
> @@ -142,6 +142,48 @@ all_caps_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
>  static struct kobj_attribute all_caps_attr =
>  __ATTR(known_capabilities, 0444, all_caps_show, NULL);
>  
> +static ssize_t
> +timeslice_store(struct kobject *kobj, struct kobj_attribute *attr,
> +		const char *buf, size_t count)
> +{
> +	struct intel_engine_cs *engine = kobj_to_engine(kobj);
> +	unsigned long long duration;
> +	int err;
> +
> +	/*
> +	 * Execlists uses a scheduling quantum (a timeslice) to alternate
> +	 * execution between ready-to-run contexts of equal priority. This
> +	 * ensures that all users (though only if they of equal importance)
> +	 * have the opportunity to run and prevents livelocks where contexts
> +	 * may have implicit ordering due to userspace semaphores.
> +	 */
> +
> +	err = kstrtoull(buf, 0, &duration);
> +	if (err)
> +		return err;
> +
> +	if (duration > jiffies_to_msecs(MAX_SCHEDULE_TIMEOUT))
> +		return -EINVAL;
> +
> +	WRITE_ONCE(engine->props.timeslice_duration_ms, duration);
> +
> +	if (execlists_active(&engine->execlists))
> +		set_timer_ms(&engine->execlists.timer, duration);
> +
> +	return count;
> +}
> +
> +static ssize_t
> +timeslice_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
> +{
> +	struct intel_engine_cs *engine = kobj_to_engine(kobj);
> +
> +	return sprintf(buf, "%lu\n", engine->props.timeslice_duration_ms);
> +}
> +
> +static struct kobj_attribute timeslice_duration_attr =
> +__ATTR(timeslice_duration_ms, 0644, timeslice_show, timeslice_store);
> +
>  static void kobj_engine_release(struct kobject *kobj)
>  {
>  	kfree(kobj);
> @@ -206,6 +248,10 @@ void intel_engines_add_sysfs(struct drm_i915_private *i915)
>  		if (sysfs_create_files(kobj, files))
>  			goto err_object;
>  
> +		if (intel_engine_has_timeslices(engine) &&
> +		    sysfs_create_file(kobj, &timeslice_duration_attr.attr))
> +			goto err_engine;
> +
>  		if (0) {
>  err_object:
>  			kobject_put(kobj);