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@xxxxxxxxxxxxxxxxxx>
CC: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
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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