Re: [PATCH] Optimize int_sqrt for small values for faster idle

[Andi Kleen]

On Mon, Feb 01, 2016 at 10:25:17PM +0100, Rasmus Villemoes wrote:
> On Thu, Jan 28 2016, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> 
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> >
> > The menu cpuidle governor does at least two int_sqrt() each time
> > we go into idle in get_typical_interval to compute stddev
> >
> > int_sqrts take 100-120 cycles each. Short idle latency is important
> > for many workloads.
> >
> 
> If you want to optimize get_typical_interval(), why not just take the
> square root out of the equation (literally)?
> 
> Something like

Looks good. Yes that's a better fix.

-Andi