[PATCH v3] powerpc: strstr optimization

[Ondřej Bílka]

On Thu, Jul 16, 2015 at 04:16:12PM -0400, Carlos O'Donell wrote:
> On 07/16/2015 03:55 PM, Ondřej Bílka wrote:
> > On Wed, Jul 15, 2015 at 09:40:00PM -0400, Carlos O'Donell wrote:
> >> On 07/15/2015 08:43 PM, Carlos O'Donell wrote:
> >>>> May I proceed with this commit?
> >>>
> >>> Yes, please commit this for 2.22.
> >>
> >> For the record I trust IBM to make sure these patches make incremental
> >> improvements in performance even if they are not the best possible
> >> performance as pointed out by Ondrej Bilka.
> >>
> > Sorry Carlos, your trust is misplaced. This patch wasn't reviewed at
> > all. I did that as test how much we could test IBM to verify patches. 
> > 
> > I pointed out that it could have possibly quadratic behaviour which
> > still does. So please don't accept unreviewed patches next time.
> 
> They showed cases for which the code does go faster and objectively
> so using the microbenchmark, and that's a win for now. Please continue 
> to work with IBM to remove the quadratic worst case.
>
Carlos, that benchmark lack consensus. When I wrote it at thread it was
explicitly mentioned as counterexample why it shouldn't be used. Florian
raised objection that strstr isn't used on random inputs.

Also I don't think that its 'objective' benchmark at all, for example it
never measures case when we find string could happen relatively often
when user knows that string is there.