On Thu, 3 Jun 2010, Arjan van de Ven wrote:
On Thu, 3 Jun 2010 19:26:50 -0700 (PDT)
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
If the system is idle (or almost idle) for long times, I would
heartily recommend actively shutting down unused cores. Some CPU's
are hopefully smart enough to not even need that kind of software
management, but I suspect even the really smart ones might be able to
take advantage of the kernel saying: "I'm shutting you down, you
don't have to worry about latency AT ALL, because I'm keeping another
CPU active to do any real work".
sadly the reality is that "offline" is actually the same as "deepest C
state". At best.
As far as I can see, this is at least true for all Intel and AMD cpus.
And because there's then no power saving (but a performance cost), it's
actually a negative for battery life/total energy.
I believe that this assumes you are in the 'race to idle' situation where
when you finish your work you can shutdown. If the work is ongoing you may
never shutdown.
Also, what about the new CPUs where you can ramp up the clockspeed on some
cores if you hsut down other cores? that couls also benifit individual
threads.
David Lang
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