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From:   Nathan Moinvaziri <nathan@nathanm.com>
To:     Andy Shevchenko <andy@kernel.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering if
 chars match
Thread-Topic: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering
 if chars match
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Date:   Tue, 25 Oct 2022 17:53:49 +0000
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Hi Andy,

I appreciate your quick feedback!

I have done as you suggested and published my results this time using Googl=
e benchmark:
https://github.com/nmoinvaz/strcasecmp

After you review it, and if you still think the patch is worthwhile then I =
can fix the other problems you mentioned for the original patch. If you thi=
nk it is not worth it, then I understand.=20

Thanks again,
Nathan

-----Original Message-----
From: Andy Shevchenko <andy@kernel.org>=20
Sent: Tuesday, October 25, 2022 2:04 AM
To: Nathan Moinvaziri <nathan@nathanm.com>
Cc: linux-kernel@vger.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@nathanm.com> wr=
ote:

...

> > When running tests using Quick Benchmark with two matching 256=20
> > 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=20
> numbers. Can we see those, please?

So, I have read carefully and see the reference to some QuickBenchmark I ha=
ve 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 thei=
r machines. You also missed details about how you run, what the data set ha=
s been used, etc.

> Note, that you basically trash CPU cache lines when characters are not=20
> equal, and before doing that you have a branching. I'm unsure that=20
> your way is more performant than the original one.

--
With Best Regards,
Andy Shevchenko