[Intel-gfx] [PATCH v2 1/3] drm/i915: Break busywaiting for requests on pending signals

[Tvrtko Ursulin]

On 27/11/15 14:26, Chris Wilson wrote:
> The busywait in __i915_spin_request() does not respect pending signals
> and so may consume the entire timeslice for the task instead of
> returning to userspace to handle the signal.
>
> In the worst case this could cause a delay in signal processing of 20ms,
> which would be a noticeable jitter in cursor tracking. If a higher
> resolution signal was being used, for example to provide fairness of a
> server timeslices between clients, we could expect to detect some
> unfairness between clients (i.e. some windows not updating as fast as
> others). This issue was noticed when inspecting a report of poor
> interactivity resulting from excessively high __i915_spin_request usage.
>
> Fixes regression from
> commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2]
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date:   Tue Apr 7 16:20:41 2015 +0100
>
>       drm/i915: Optimistically spin for the request completion
>
> v2: Try to assess the impact of the bug

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko