Re: A few questions and issues with dynticks, NOHZ and powertop

From: Arjan van de Ven
Date: Mon Apr 05 2010 - 12:23:45 EST

On 4/5/2010 9:22, Paul E. McKenney wrote:
On Mon, Apr 05, 2010 at 09:07:33AM -0700, Arjan van de Ven wrote:
On 4/5/2010 8:14, Paul E. McKenney wrote:
So the main issue is that for many workloads, it is best to run full bore
and get done quickly, thus allowing the entire machine to be powered down?


If so, it seems likely that there would be some workloads that were sometimes
unable to use all the CPUs, in which case shutting down (idling, offlining,
dyntick-idling, whatever) the excess CPUs might nevertheless be the right
thing to do.

but the point is that the normal scheduler + idle behavior gives you exactly that
in a natural way !
If you don't have enough work (tasks) to keep all cores busy, the others are and stay idle.

So your earlier objection was not to dyntick-idle as such, but rather
to artificially constraining the scheduler to induce dyntick-idle?

my objection was against the notion that offlining cpus helps power/energy ;-)

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