Messages in this thread | | | Date | Wed, 31 Jul 2019 19:32:26 +0200 | From | Pavel Machek <> | Subject | Re: [RFC v4 0/8] TurboSched: A scheduler for sustaining Turbo Frequencies for longer durations |
| |
Hi!
> >> Abstract > >> ======== > >> > >> The modern servers allows multiple cores to run at range of frequencies > >> higher than rated range of frequencies. But the power budget of the system > >> inhibits sustaining these higher frequencies for longer durations. > > > > Thermal budget? > > Right, it is a good point, and there can be possibility of Thermal throttling > which is not covered here. > But the thermal throttling is less often seen in the servers than the throttling > due to the Power budget constraints. Also one can change the power cap which leads > to increase in the throttling and task packing can handle in such > cases.
Ok. I thought you are doing this due to thermals. If I understand things correctly, you can go over thermal limits for a few seconds before the silicon heats up. What is the timescale for power budget?
> BTW, Task packing allows few more cores to remain idle for longer time, so > shouldn't this decrease thermal throttles upto certain extent?
I guess so, yes.
> > >> These numbers are w.r.t. `turbo_bench.c` multi-threaded test benchmark > >> which can create two kinds of tasks: CPU bound (High Utilization) and > >> Jitters (Low Utilization). N in X-axis represents N-CPU bound and N-Jitter > >> tasks spawned. > > > > Ok, so you have description how it causes 13% improvements. Do you also have metrics how > > it harms performance.. how much delay is added to unimportant tasks etc...? > > > > Yes, if we try to pack the tasks despite of no frequency throttling, we see a regression > around 5%. For instance, in the synthetic benchmark I used to show performance benefit, > for lower count of CPU intensive threads (N=2) there is -5% performance drop. > > Talking about the delay added to an unimportant tasks, the result can be lower throughput > or higher latency for such tasks.
Thanks. I believe it would be good to mention disadvantages in the documentation, too.
Best regards, Pavel
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html [unhandled content-type:application/pgp-signature] | |