Re: [RFC][PATCH] Runtime switching of the idle function [take 2]

[Ingo Molnar <mingo@elte.hu>]

* Andrew Morton <akpm@osdl.org> wrote:

> > The way to solve this was to set
> >  idle=poll.  The original patch I sent was to allow the user to change to
> >  idle=poll dynamically.  This way they could switch to the poll_idle and
> >  run there tests (requiring tsc not to drift) and then switch back to the
> >  default idle to save on electricity.
> 
> Use gettimeofday()?
> 
> If it's just for some sort of instrumentation, run NR_CPUS instances 
> of a niced-down busyloop, pin each one to a different CPU?  That way 
> the idle function doesn't get called at all..

idle=poll is also frequently done for performance reasons [it reduces 
idle wakeup latency by 10 usecs] - while it could be turned off if the 
system has been idle for some time. E.g. cpufreqd could sample idle time 
and turn on/off idle=poll. High-performance setups could enable it all 
the time.

as long as it can be done with zero-cost, i dont see why Steven's patch 
wouldnt be a plus for us. It's a performance thing, and having runtime 
switches for seemless performance features cannot be bad.

	Ingo