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

From: Arjan van de Ven
Date: Mon Apr 05 2010 - 15:49:15 EST

On 4/5/2010 11:44, david@xxxxxxx wrote:
On Mon, 5 Apr 2010, 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
and get done quickly, thus allowing the entire machine to be powered


Race To Idle works extremely well in a batch type situation where there
is not going to be any work to do after you finish what you have.

It doesn't work quite as well if you are going to have new work to do in
the near future.

You cannot power down the entire machine if you have to look for user

It takes time (and power) to shut down and start back up, if you are
going to have more work to do before you can make the complete cycle
(and save more power than it costs to make the transitions), it's best
to stay at full power, even if you are idle.

for the things we're talking about here (memory controllers etc) we're talking
about single to low double digit microseconds (or even less) of time to go up and down.
Many of the things you talk about are in the millisecond timeframe.

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