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Re: [PATCH v3] powerpc: strstr optimization
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>, GNU C Library <libc-alpha at sourceware dot org>, Steve Munroe <sjmunroe at us dot ibm dot com>, Rajalakshmi Srinivasaraghavan <raji at linux dot vnet dot ibm dot com>
- Date: Thu, 16 Jul 2015 16:16:12 -0400
- Subject: Re: [PATCH v3] powerpc: strstr optimization
- Authentication-results: sourceware.org; auth=none
- References: <558A5642 dot 5020107 at linux dot vnet dot ibm dot com> <558A5761 dot 2000409 at linux dot vnet dot ibm dot com> <87oajpm8nc dot fsf at totoro dot br dot ibm dot com> <871tgijuri dot fsf at linux dot vnet dot ibm dot com> <55A6FE3F dot 6090701 at redhat dot com> <55A70B70 dot 6090607 at redhat dot com> <20150716195538 dot GA5140 at domone>
On 07/16/2015 03:55 PM, OndÅej BÃlka 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?
Cheers,
Carlos.