On 16/11/15 11:22, Chris Wilson wrote:
On Mon, Nov 16, 2015 at 09:54:10AM +0000, Tvrtko Ursulin wrote:
Hi,
On 15/11/15 13:32, 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.
Obviously correct to break the spin, but if spending a jiffie to react to signals was the only problem then it is not too severe.
Add something to the commit message about how it was found/reported and about the severity of impact, etc?
Perhaps:
At 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. This issue was noticed when inspecting a report of poor interactivity resulting from excessively high __i915_spin_request usage.
Oh its the Xorg scheduler tick... I always forget about that. Was thinking that it is only about fatal, or at least infrequent signals.
Regards,
Tvrtko