On Thu, Mar 12, 2015 at 03:18:01PM +0000, Tvrtko Ursulin wrote: > On 03/12/2015 01:18 PM, Chris Wilson wrote: > >1ms. I was just thinking of doing USECS_PER_SEC / HZ, then realised that > >was a jiffie, hence the confusion. At any rate, it is still the minimum > >we can trivially wait for (without an expensive hrtimer). > > Unless I lost track with the times, that's CONFIG_HZ right? > > I don't know what server distributions do, but this Ubuntu LTS I am > running has HZ=250 which means 4ms. > > That would mean on a system where throughput is more important than > latency, you lose most throughput by spinning the longest. In theory > at least, no? Only in theory, and only if you mean throughput of non-i915 workloads with preemption disabled. Spinning here improves both latency and throughput for gfx clients. Using up the timeslice for the client may have secondary effects though - otherwise they would get iowait credits. > So perhaps which should be a tunable? Optionally auto-select the > initial state based on HZ. Spinning less than a jiffie requires hrtimers at which point you may as well just use the i915 interrupt (rather than setup a timer interrupt). -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
