On Wed, 16 Mar 2016 16:38:56 -0700 Joel Fernandes <agnel.j...@gmail.com> wrote:
> I am not sure if the problem is with the i915 driver, because the > mutex spin on owner stuff is mutex related so the mutex design may > potentially need a tweak (I mentioned a proposal of adding mutex > spinning time outs). > Also since this is latency issue related (I mentioned preemptoff > tracer and preempt disabled), I sent it to linux-rt-users. Thanks for > the tip about sending it to i915 developers, incase no one here has a > say in the matter, I can drop them a note later as well. Actually, the preempt off section here is not really an issue: rcu_read_lock(); while (owner_running(lock, owner)) { if (need_resched()) break; cpu_relax_lowlatency(); } rcu_read_unlock(); Although preemption may be disabled, that "need_resched()" check will break out of the loop if a higher priority task were to want to run on this CPU. I probably should add a hook there to let the preemptoff tracer know that this is not an issue. Thanks for the report. -- Steve