Re: [RFC] (How to) Let idle CPUs sleep

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

On Fri, May 13, 2005 at 08:29:17AM +0000, Nick Piggin wrote:
> And don't forget that the watchdog approach can just as easily deep
> sleep a CPU only to immediately wake it up again if it detects an
> imbalance.

I think we should increase the threshold beyond which the idle CPU
is woken up (more than the imbalance_pct that exists already). This
should justify waking up the CPU.

> And the CPU usage / wakeup cost arguments cut both ways. The busy
> CPUs have to do extra work in the watchdog case.

Maybe with a really smart watchdog solution, we can cut down this overhead.
I did think of other schemes - a dedicated CPU per node acting as watchdog 
for that node and per-node wacthdog kernel threads? - to name a few. What I had
proposed was the best I thought. But maybe we can look at improving it 
to see if the overhead concern you have can be reduced - meeting the interests
of both the worlds :)


-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017