[Intel-gfx] [PATCH] drm/i915: Queue page flip work with high priority
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Tue Sep 13 11:12:03 UTC 2016
On 13/09/16 11:31, Imre Deak wrote:
> On ti, 2016-09-13 at 11:24 +0100, Tvrtko Ursulin wrote:
>> On 12/09/16 15:09, Imre Deak wrote:
>>> While user space has control over the scheduling priority of its
>>> page
>>> flipping thread, the corresponding work the driver schedules for
>>> MMIO
>>> flips always runs with normal scheduling priority. This would
>>> hinder an
>>> application that wants more stringent guarantees over flip timing
>>> (to
>>> avoid missing a flip at the next frame count).
>>>
>>> Fix this by scheduling the work with high priority, meaning normal
>>> scheduling policy with -20 nice level.
>>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97775
>>> Testcase: igt/kms_cursor_legacy
>>> CC: Chris Wilson <chris at chris-wilson.co.uk>
>>> CC: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>> Signed-off-by: Imre Deak <imre.deak at intel.com>
>>> ---
>>> drivers/gpu/drm/i915/i915_drv.c | 7 +++++++
>>> drivers/gpu/drm/i915/i915_drv.h | 4 ++++
>>> drivers/gpu/drm/i915/intel_display.c | 2 +-
>>> 3 files changed, 12 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_drv.c
>>> b/drivers/gpu/drm/i915/i915_drv.c
>>> index 02c34d6..381ef23 100644
>>> --- a/drivers/gpu/drm/i915/i915_drv.c
>>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>>> @@ -756,8 +756,14 @@ static int i915_workqueues_init(struct
>>> drm_i915_private *dev_priv)
>>> if (dev_priv->hotplug.dp_wq == NULL)
>>> goto out_free_wq;
>>>
>>> + dev_priv->flip_wq = alloc_workqueue("i915-flip",
>>> WQ_HIGHPRI, 0);
>>> + if (dev_priv->flip_wq == NULL)
>>> + goto out_free_dp_wq;
>>> +
>>> return 0;
>>>
>>> +out_free_dp_wq:
>>> + destroy_workqueue(dev_priv->hotplug.dp_wq);
>>> out_free_wq:
>>> destroy_workqueue(dev_priv->wq);
>>> out_err:
>>> @@ -768,6 +774,7 @@ out_err:
>>>
>>> static void i915_workqueues_cleanup(struct drm_i915_private
>>> *dev_priv)
>>> {
>>> + destroy_workqueue(dev_priv->flip_wq);
>>> destroy_workqueue(dev_priv->hotplug.dp_wq);
>>> destroy_workqueue(dev_priv->wq);
>>> }
>>> diff --git a/drivers/gpu/drm/i915/i915_drv.h
>>> b/drivers/gpu/drm/i915/i915_drv.h
>>> index f499fa5..3653ce4 100644
>>> --- a/drivers/gpu/drm/i915/i915_drv.h
>>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>>> @@ -1844,6 +1844,10 @@ struct drm_i915_private {
>>> * result in deadlocks.
>>> */
>>> struct workqueue_struct *wq;
>>> + /**
>>> + * flip_wq - High priority flip workqueue.
>>> + */
>>> + struct workqueue_struct *flip_wq;
>>>
>>> /* Display functions */
>>> struct drm_i915_display_funcs display;
>>> diff --git a/drivers/gpu/drm/i915/intel_display.c
>>> b/drivers/gpu/drm/i915/intel_display.c
>>> index 3c367d0..48433e1 100644
>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>> @@ -12278,7 +12278,7 @@ static int intel_crtc_page_flip(struct
>>> drm_crtc *crtc,
>>>
>>> work->flip_queued_req = i915_gem_active_get(&obj-
>>>> last_write,
>>> &obj-
>>>> base.dev->struct_mutex);
>>> - schedule_work(&work->mmio_work);
>>> + queue_work(dev_priv->flip_wq, &work->mmio_work);
>>> } else {
>>> request = i915_gem_request_alloc(engine, engine-
>>>> last_context);
>>> if (IS_ERR(request)) {
>>>
>>
>> I am curious if just a dedicated wq would be enough, or you have
>> found
>> that it has to be a high-prio one?
>
> I haven't tried a dedicated normal-prio wq. Right, another work in the
> queue could also hold up this one, but the system_wq is unordered, so
> that kind of dependency shouldn't be a problem if that's what you
> meant.
Yes, I've suspicious whether the problem is work start latency and not
actually the worker priority. Since the flip work item mostly does
waiting and little CPU activity, I though the former sounded like more
likely.
Regards,
Tvrtko
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