linux-kernel - Re: [PATCH v1 1/1] lib/string: Use strchr() in strpbrk()

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Date:   Sat, 28 Jan 2023 21:54:44 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andy@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 1/1] lib/string: Use strchr() in strpbrk()

On Sat, Jan 28, 2023 at 4:51 PM David Laight <David.Laight@...lab.com> wrote:
>
> From: Andy Shevchenko
> > Sent: 27 January 2023 15:52
> >
> > Use strchr() instead of open coding it as it's done elsewhere in
> > the same file. Either we will have similar to what it was or possibly
> > better performance in case architecture implements its own strchr().
>
> Except that you get a whole load of calls to strchr() for (typically)
> very few characters.
> So the cost of the calls dominates, anything that tries to speed up
> strchr() for long strings will also slow things down.

Hmm... I haven't seen the calls, I assume gcc simply inlined a copy of that.

...

> Although I very much doubt strpbrk() is used anywhere where
> performance matters.

strsep()/strspn() are the users.

-- 
With Best Regards,
Andy Shevchenko