On Mon, 23 Jul 2007, Ondrej Zajicek wrote:
On Sun, Jul 22, 2007 at 09:19:17PM -0700, Arjan van de Ven wrote:
let me give you a real world example then, and the numbers I'm using are
ballpark the same as you'll find in a (mobile) core 2 duo datasheet, I
just rounded them a little so that the math works out nice.
power at full speed: 34W
power at half speed: 24W
power at idle: 1W
I have usually seen different numbers, for example:
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/30430.pdf
Although this paper speaks about thermal design power instead of power
consumption, i suppose that it should be roughly equal.
For example Athlon 64 3700 (ADA3700AEP5AR):
2.4 GHz, 1.5 V -> 89 W
2.2 GHz, 1.4 V -> 72 W
2.0 GHz, 1.3 V -> 53 W
1.8 GHz, 1.2 V -> 39 W
1.0 GHz, 1.1 V -> 22 W
Even my measurement on PC (Athlon X2, VIA K8T890) of complete PC power
consumption shows that it is more efficient to be busy for 2 time units
on 1 GHz than be busy for 1 time unit and be idle for 1 time unit
on 2 GHz.
1 GHz:
both cores idle: 48 W
one core busy: 57 W
two cores busy: 66 W
2 GHz:
both cores idle: 54 W
one core busy: 78 W
two cores busy: 95 W
what Arjan is saying is one time unit at 2GHz with both cores busy, one
time unit at 1GHz with both cores idle (this would be 132w/two time units
vs 143W/two time units) still a win for running a 1GHz, but a smaller one
or better still, one time unit at 2GHz with both cores busy, one time unit
in sleep mode, in this case if the sleep mode is any good at all it wins.
David Lang
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