The PowerClamp driver

Posted Mar 7, 2013 21:57 UTC (Thu) by pjones (subscriber, #31722)
In reply to: The PowerClamp driver by redden0t8
Parent article: The PowerClamp driver

energy = power * time. If you deliberately hobble the workload to use less power, it takes more time, but also operates less efficiently. This means you'll use more energy.

The PowerClamp driver

Posted Mar 7, 2013 22:53 UTC (Thu) by dgm (subscriber, #49227) [Link] (3 responses)

> If you deliberately hobble the workload to use less power, it takes more time

Not if your work depends on external events, that is, IO. And it all depends on the characteristics of the system. If you can do it 10% slower at half the power consumption, it may very well be worth the wait.

The PowerClamp driver

Posted Mar 7, 2013 23:30 UTC (Thu) by dlang (guest, #313) [Link] (2 responses)

and remember that even memory access is an external event that is significantly slower than the CPU, so if what you are doing is a small amount of computation on a large amount of memory, you may be able to do it in the same amount of time with a much slower CPU.

The PowerClamp driver

Posted Mar 11, 2013 13:06 UTC (Mon) by ssam (guest, #46587) [Link] (1 responses)

if i am running a process that is limited by memory bandwidth, wont the CPU be spend lots of time idle, and so reducing the power consumption already? Can the CPU sleep while it is waiting for something to be fetched from RAM?

The PowerClamp driver

Posted Mar 11, 2013 20:28 UTC (Mon) by dlang (guest, #313) [Link]

not really, it takes a long time for the processor to go to sleep and wake up again, long enough that it's frequently better for the processor to idle at high speed rather than go into sleep mode.