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

[Chris Wilson]

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