Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations

From	Andy Shevchenko <andy.shevchenko@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations
Date	2017-06-08 03:50 +0200
Message-ID	<tPUKe-65e-7@gated-at.bofh.it> (permalink)
References	<tPK8a-7Mn-21@gated-at.bofh.it> <tPKhR-7Rr-43@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Wed, Jun 7, 2017 at 5:29 PM, Matthew Wilcox <willy@infradead.org> wrote:

> Commit 7dd968163f ("bitmap: bitmap_equal memcmp optimization") was
> rather more restrictive than necessary; we can use memcmp() to implement
> bitmap_equal() as long as the number of bits can be proved to be a
> multiple of 8.  And architectures other than s390 may be able to make
> good use of this optimisation.

> -       if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0)
> +       if (__builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
>                 return !memcmp(src1, src2, nbits / 8);

I'm not sure this is a fully correct change.
What exactly ' & 7' part does?
For me looks like you may just drop it.

-- 
With Best Regards,
Andy Shevchenko

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-06-08 03:50 +0200
  Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations Matthew Wilcox <willy@infradead.org> - 2017-06-08 05:00 +0200
    Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-06-08 14:40 +0200
      Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2017-06-08 15:50 +0200
        Re: [PATCH 3/3] bitmap: Use memcmp optimisation in more situations Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-06-08 16:50 +0200

csiph-web