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Re: [PATCH v3] powerpc: strstr optimization
- From: Steven Munroe <munroesj at linux dot vnet dot ibm dot comcom>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: "Carlos O'Donell" <carlos at redhat dot com>, OndÅej BÃlka <neleai at seznam dot cz>, 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: Wed, 22 Jul 2015 12:59:00 -0500
- Subject: Re: [PATCH v3] powerpc: strstr optimization
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- Reply-to: munroesj at linux dot vnet dot ibm dot com
On Wed, 2015-07-22 at 16:12 +0000, Joseph Myers wrote:
> On Thu, 16 Jul 2015, Carlos O'Donell wrote:
> > 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?
> 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
There is a denial of service attach here, but not what you would think.
Effectively this (noise and FUD) is blocking my team from submitting
patches and preventing my team for moving on to additional optimization.
The core problem is that there is no object definition of what a
quadratic behavior might be, nor has a certain troll that constantly
shouts (quadratic! quadratic! quadratic!) about this, provided objective
proof, in the form of benchmark.
So if you really believe that this is problem, you should insist on a
objective benchmark and apply that objective standard to every platform.
This would allow my team work on the problem and improve our code even
Otherwise you are just wasting every ones time.