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

[Eric Dumazet]

On Thu, 2017-07-20 at 12:10 +0200, Peter Zijlstra wrote:
> On Mon, Feb 01, 2016 at 04:36:38PM -0800, Eric Dumazet wrote:
> > On Tue, 2016-02-02 at 00:08 +0100, Rasmus Villemoes wrote:
> > 
> > > Thanks. (Is there a good way to tell gcc that avg*avg is actually a
> > > 32x32->64 multiplication?)
> > 
> > If avg is 32bit, compiler does that for you.
> > 
> > u32 avg = ...
> > 
> > u64 result = (u64)avg * avg;
> 
> It does not in fact do that :/ See commit:
> 
>   9e3d6223d209 ("math64, timers: Fix 32bit mul_u64_u32_shr() and friends")

Interesting :/

Thanks for letting me know !