Michael Pogue wrote: > Hmmm...I believe that T-states will still always save power, though, > while the CPU is executing instructions. If the slowdown is acceptable, > I'm not sure why this method would not be a useful way to consume > less power. > > Here's an example, based on the data I sent earlier: > > Let's say we have a task that takes 1 CPU minute of time (at full power, > no throttle), and we need to execute it once every 10 minutes. Look at > the second table -- the largest entry under 10 minutes is 8.44 > minutes (P3/75% throttle). > > So, if we ran that box at P3/75% for 8.44 minutes, and P3/100% (C1, > essentially) total power consumption would be about: > > 36.25*8.5 + 34*1.5 = 359 W-min. > > That's a better choice (about 4% better) than running P0/0% for 1 minute > and P3/100%(C1) for 9 minutes, which would consume about: > > 67*1 + 34*9 = 373 W-min. > > Based on these measurements, at least, it seems to me that for a given > P-state, throttling could always save *some* power on this machine (as long > as we're still OK with the additional slowdown, which has to be the case > for any power/frequency manipulation, as Dana implied). > > Does this meet the definition of "same amount of work in the same amount > of time, while consuming less energy"? I think it does. :-) Yes, but I believe that you could run have the job at P3/0% for 2.11 minutes and then P3/100%(C1) for 7.89 minutes:
43*2.11 + 34*7.89 = 359 W-min In other words, it was P3 that got the work done while consuming less power. All throttling did for you was increase the amount of time to get the work done, right? Mark > > Mike > > Andrei Dorofeev wrote: >> On 10/30/07, Dana H. Myers <Dana.Myers at sun.com> wrote: >>>> I would agree with Aubrey that T-states don't save power if by "save" we >>>> mean that we can do the same amount of work at the same amount of time >>>> while consuming less energy. >>> I don't think P-states meet this definition of saving power, either, do >>> they? >> Actually, I think P-states can be (at least theoretically) used in such a way >> that this definition is met. In an ideal environment where we know precisely >> what are the requirements in terms of CPU cycles of a given workload, we >> can afford putting CPU into lower FID/VID without loosing performance and >> increasing run times while saving power. Attempting to do the same thing >> with T-states will not save any power because we're going to stay in C1 with >> or without T-states. Also, just spending C1 time in lowest P-state alone >> can save power on AMD CPUs which don't automatically drop >> frequencies/voltages upon entering C1 (which is what C1E on Intel CPUs is >> for). >> >> - Andrei >> _______________________________________________ >> tesla-dev mailing list >> tesla-dev at opensolaris.org >> http://mail.opensolaris.org/mailman/listinfo/tesla-dev > _______________________________________________ > tesla-dev mailing list > tesla-dev at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/tesla-dev
