[Codel] fp sqrt vis int sqrt?

[Eric Dumazet]

On Fri, 2012-05-04 at 11:26 -0400, Jim Gettys wrote:

> 
> I suspect there are fully integer implementations kicking around... 
> It's just that x86 finally got fast enough FP that doing one multiply in
> floating point beat the alternative.

Anyway we dont need to compute sqrt() at all.

This can be done easily when we do the q->count++, if we hold in
q->sqrt_count the estimated value of sqrt(count)

Ie replace :

q->count++;

by:

q->count++;
n = q->sqrt_count + 1;
if (n * n <= q->count)
	q->sqrt_count = n;

A multiply is an acceptable cost.


Of course, you need to reset sqrt_count to 1 when count is reset to 1