linux-kernel - Re: Re [PATCH v2] lib: optimize cpumask_next

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Date:   Wed, 25 Oct 2017 20:41:46 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Clement Courbet <courbet@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ingo Molnar <mingo@...nel.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re [PATCH v2] lib: optimize cpumask_next_and()

On Wed, Oct 25, 2017 at 06:50:14PM +0300, Yury Norov wrote:
> On Wed, Oct 25, 2017 at 05:28:41PM +0200, Clement Courbet wrote:
> > Thanks for the comments Yury.
> > 
> > > But I'd like also to keep _find_next_bit() consistent with
> > > _find_next_bit_le()
> > 
> > Not sure I understand what you're suggesting here: Do you want a
> > find_next_and_bit_le() or do you want to make _find_next_bit_le() more
> > like _find_next_bit() ? In the latter case we might just want to merge
> > it with _find_next_bit() and end up with an extra is_le parameter :)
> 
> Both ways will work, but I think that extra is_le is too much.
> _find_next_bit_le() should be the copy of _find_next_bit() with the
> addition of swapping code.
> 
> If you don't need find_next_and_bit_le(), don't add it.
> find_{first,last}_bit() doesn't have LE version, for example.

Few comments more.

_find_next_bit is now referenced also by find_next_and_bit(), and
so it should be added to guard code:

#if !defined(find_next_bit) || !defined(find_next_zero_bit)
        || !defined(find_next_and_bit)
static unsigned long _find_next_bit( ... )
{
        ...
}
#endif

It may be essential at least for arm.

Don't forget to synchronize your changes with
tools/lib/find_bit.c

Thanks,
Yury