[Intel-gfx] [PATCH v3] drm/i915: Queue page flip work via a low latency, unbound workqueue

[Chris Wilson]

On Tue, Sep 20, 2016 at 02:58:19PM +0300, 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 from the generic system workqueue which has some
> scheduling overhead due it being CPU bound. 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 from the unbound system workqueue
> which provides for minimal scheduling latency.
> 
> v2:
> - Use an unbound workqueue instead of a high-prio one. (Tvrtko, Chris)
> v3:
> - Use the system unbound wq instead of a dedicated one. (Maarten)
> 
> 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>
> CC: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com> (v1)

We violate the unbound_wq rules no worse than the ordinary system_wq,
and this brings mmioflip on a par with nonblocking atomic modesets, so
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre