Re: [PATCH 2/2] drm/i915: Use atomic waits for short non-atomic ones

Chris Wilson
2016-06-28T14:15:03Z

On Tue, Jun 28, 2016 at 02:55:28PM +0100, Chris Wilson wrote:
> On Tue, Jun 28, 2016 at 02:29:33PM +0100, Tvrtko Ursulin wrote:
> > How would you implement it with cpu_clock? What would you do when
> > re-scheduled?
>
> unsigned long base;
> int cpu;
> int ret;
>
> preempt_disable();
> cpu = smp_processor_id();
> base = local_clock() >> 10;
> for (;;) {
> u64 now = local_clock() >> 10;
> preempt_enable();
>
> if (COND) {
> ret = 0;
> break;
> }
>
> if (now - base >= timeout) {
> ret = -ETIMEOUT;
> break;
> }
>
> cpu_relax();
>
> preempt_disable();
> if (unlikely(cpu != smp_processor_id()) {
> timeout -= now - base;

For this, we should scale everything to ns (u64).
-Chris

--
Chris Wilson, Intel Open Source Technology Centre