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@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
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@xxxxxxxxx>
Tested-by: Steve Carbonari <steven.carbonari@xxxxxxxxx
> ---
> 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, ×lice_duration_attr.attr))
> + goto err_engine;
> +
> if (0) {
> err_object:
> kobject_put(kobj);
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