Re: [PATCH 5/5] kvm: optimize GFN to memslot lookup with large slots amount

Radim Krčmář
2014-12-02T21:03:09Z

2014-12-02 19:45+0100, Paolo Bonzini:
> On 02/12/2014 18:33, Radim Krčmář wrote:
> >> > + while (start < end) {
> >> > + slot = start + (end - start) / 2;
> >> > +
> >> > + if (gfn >= memslots[slot].base_gfn)
> > (Even thought division is costly, I think that checking here if 'slot'
> > is the one we want wouldn't help very much.)
> >
>
> Division by an unsigned is just a right shift. Division by signed
> integer is a right shift + conditional move. We can change / 2 to
> explicit >> 1, or change start and end to unsigned, or both.

My bad, no respectable optimizer would miss that.