[PATCH v3] powerpc: strstr optimization

[Carlos O'Donell]

On 07/22/2015 12:12 PM, Joseph Myers wrote:
> On Thu, 16 Jul 2015, 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.
>>
>> Tulio, You will need to work out why you have quadratic worst case.
>> It's certainly something we try to avoid. Did you make a particular
>> decision not to avoid it?
> 
> If there's a quadratic worst case newly introduced for 2.22, I'd consider 
> that a security hole (denial of service) that needs to block the release 
> of 2.22 until it's fixed (possibly by removing the implementation in 
> question).

Joseph,

We have had quadratic worse case in our string routines for years without
it blocking a release. I agree that it is not the best case for a release
to have such behaviour, but should it block this release?

Florian,

I would like to hear your opinion on whether you might consider this a
security issue, or simply a QoI issue.

Tulio,

Could you please review the possibility of quadratic behaviour and respond
prompty? I don't want this to hold up the release.

Cheers,
Carlos.