Eric Saxe wrote: > David Vengerov wrote: >> Eric Saxe wrote: >> >>> David Vengerov wrote: >>> >>>> Eric Saxe wrote: >>>> >>>>> If there are N or more running threads in an N-CPU system, then >>>>> utilization is at 100%. Generally, i'm thinking that the CPUs >>>>> should all be clocked up, if we want to maximize performance. >>>>> There's not much opportunity to squander power in this case. It's >>>>> really only the "partial utilization" scenario, where power is >>>>> being directed at the part of the system that isn't being used. >>>> >>>> If you hold this view, then the policy I described previously that >>>> decides on the clock rate of idle CPUs based on how their number >>>> has fluctuated in the past should be very relevant and allows us to >>>> find the desired tradeoff between maximizing the the system's >>>> performance (by never clocking down the idle CPUs) and minimizing >>>> the power consumption (by running idle CPUs at the lowest power and >>>> increasing their clock rate only when they receive some threads). >>>> The policy I am envisioning should be able to clock down CPUs to >>>> different extents based on estimated probabilities of some of them >>>> receiving threads in the near future. >>> >>> >>> Where I think this is especially relevant is where there exists a >>> non-trivial amount of time to bring online additional resources >>> (latency). If ML techniques can help predict when utilization will >>> increase/decrease, then perhaps the latency associated with bringing >>> online/offline the additional capacity can be better hidden. In the >>> data center context, where the unit of power management may be >>> suspended / powered off systems, this could be significant. >> >> Right. What latency do you expect in AMD and Intel systems? > > For P-state (frequency/voltage scaling) of processors, I believe the > latencies involved are very low. Doesn't it depend on the specific chip? I believe the Intel Enhanced Speed Step are pretty quick to change state, but Opteron changes are more involved. Mark - any observations here?
Dana
