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

[Nick Piggin]

Ingo Molnar wrote:
> * Andrew Morton <akpm@xxxxxxxx> 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.

Why not just slightly cleanup and extend (eg. to ACPI) the
hlt_counter thingy that many architectures already have?

Nick

--
SUSE Labs, Novell Inc.

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