linux-kernel - Re: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering if chars match

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y1embP5sEp/NPxK0@smile.fi.intel.com>
Date:   Tue, 25 Oct 2022 12:03:40 +0300
From:   Andy Shevchenko <andy@...nel.org>
To:     Nathan Moinvaziri <nathan@...hanm.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering
 if chars match

On Tue, Oct 25, 2022 at 11:00:36AM +0300, Andy Shevchenko wrote:
> On Tue, Oct 25, 2022 at 4:46 AM Nathan Moinvaziri <nathan@...hanm.com> wrote:

...

> > When running tests using Quick Benchmark with two matching 256 character
> > strings these changes result in anywhere between ~6-9x speed improvement.
> >
> > * We use unsigned char instead of int similar to strncasecmp.
> > * We only subtract c1 - c2 when they are not equal.

...

> You tell us that this is more preformant, but have not provided the
> numbers. Can we see those, please?

So, I have read carefully and see the reference to some QuickBenchmark I have
no idea about. What I meant here is to have numbers provided by an (open
source) tool (maybe even in-kernel test case) that anybody can test on their
machines. You also missed details about how you run, what the data set has been
used, etc.

> Note, that you basically trash CPU cache lines when characters are not
> equal, and before doing that you have a branching. I'm unsure that
> your way is more performant than the original one.

-- 
With Best Regards,
Andy Shevchenko