Messages in this thread | | | Date | Tue, 25 Oct 2022 21:55:26 +0200 | Subject | Re: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering if chars match | From | Rasmus Villemoes <> |
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On 25/10/2022 10.00, Andy Shevchenko wrote: > On Tue, Oct 25, 2022 at 4:46 AM Nathan Moinvaziri <nathan@nathanm.com> wrote: >> >> From fcb0159ee74908f92adc34143657d8ca56e9a811 Mon Sep 17 00:00:00 2001 >> From: Nathan Moinvaziri <nathan@nathanm.com> >> Date: Mon, 24 Oct 2022 16:37:59 -0700 >> Subject: [PATCH] lib/string.c: Improve strcasecmp speed by not lowering if >> chars match. > > Why is the above in the commit message? > >> With strings where many characters match exactly each character is needlessly >> converted to lowercase before comparing. This patch improves the comparison >> by only converting to lowercase after checking that the characters don't match. >> >> The more characters that match exactly the better performance we expect versus >> the old function.
> You tell us that this is more preformant, but have not provided the > numbers. Can we see those, please? > > 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. >
Are there any code paths in the kernel where strcasecmp performance matters? strcmp, sure, but strcasecmp or strncasecmp? I don't think so. If anything, we should nuke the complication in strncasecmp(), and then make strcasecmp() simply do strncasecmp(a, b, SIZE_MAX).
Rasmus
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