On 30/04/2019 10:44, Chris Wilson wrote:
When the system is idling, contention for struct_mutex should be low and
so we will be more efficient to wait for a contended mutex than
reschedule.

Signed-off-by: Chris Wilson <[email protected]>
---
  drivers/gpu/drm/i915/i915_gem_pm.c | 8 +-------
  1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_pm.c 
b/drivers/gpu/drm/i915/i915_gem_pm.c
index 3554d55dae35..3b6e8d5be8e1 100644
--- a/drivers/gpu/drm/i915/i915_gem_pm.c
+++ b/drivers/gpu/drm/i915/i915_gem_pm.c
@@ -47,13 +47,7 @@ static void idle_work_handler(struct work_struct *work)
        struct drm_i915_private *i915 =
                container_of(work, typeof(*i915), gem.idle_work.work);
- if (!mutex_trylock(&i915->drm.struct_mutex)) {
-               /* Currently busy, come back later */
-               mod_delayed_work(i915->wq,
-                                &i915->gem.idle_work,
-                                msecs_to_jiffies(50));
-               return;
-       }
+       mutex_lock(&i915->drm.struct_mutex);
intel_wakeref_lock(&i915->gt.wakeref);
        if (!intel_wakeref_active(&i915->gt.wakeref))


I don't see any real downsides to this indeed.

Reviewed-by: Tvrtko Ursulin <[email protected]>

Possible tweak could be to leave this as is, maybe just not go for the reduced idle timer on re-schedule, but add a cancel_delayed_work on the unparking side of things. That way any mutex activity without actual device unparking would only slightly delay going idle, while idle_work would retain it's minimal disturbance of the mutex.

Regards,

Tvrtko
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