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

Chris Wilson
2016-06-28T13:55:35Z

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;
cpu = smp_processor_id();
base = local_clock() >> 10;
}
}
ret;

Borrowed from udelay()
-Chris

--
Chris Wilson, Intel Open Source Technology Centre