Re: [PATCH 11/13] lib: add fast path for find_first_*_bit() and find_last_bit()

From: Yury Norov <yury.norov@gmail.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
	linux-arch@vger.kernel.org, linux-sh@vger.kernel.org,
	Alexey Klimov <aklimov@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Arnd Bergmann <arnd@arndb.de>, David Sterba <dsterba@suse.com>,
	Dennis Zhou <dennis@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Jianpeng Ma <jianpeng.ma@intel.com>,
	Joe Perches <joe@perches.com>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Rich Felker <dalias@libc.org>,
	Stefano Brivio <sbrivio@redhat.com>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH 11/13] lib: add fast path for find_first_*_bit() and find_last_bit()
Date: Tue, 6 Apr 2021 11:15:41 -0700	[thread overview]
Message-ID: <20210406181541.GA792963@yury-ThinkPad> (raw)
In-Reply-To: <20210406160327.GA180841@roeck-us.net>

On Tue, Apr 06, 2021 at 09:03:27AM -0700, Guenter Roeck wrote:
> On Mon, Mar 15, 2021 at 06:54:22PM -0700, Yury Norov wrote:
> > Similarly to bitmap functions, users would benefit if we'll handle
> > a case of small-size bitmaps that fit into a single word.
> > 
> > While here, move the find_last_bit() declaration to bitops/find.h
> > where other find_*_bit() functions sit.
> > 
> > Signed-off-by: Yury Norov <yury.norov@gmail.com>
> > ---
> >  include/asm-generic/bitops/find.h | 50 ++++++++++++++++++++++++++++---
> >  include/linux/bitops.h            | 12 --------
> >  lib/find_bit.c                    | 12 ++++----
> >  3 files changed, 52 insertions(+), 22 deletions(-)
> > 
> > diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
> > index 4148c74a1e4d..8d818b304869 100644
> > --- a/include/asm-generic/bitops/find.h
> > +++ b/include/asm-generic/bitops/find.h
> > @@ -5,6 +5,9 @@
> >  extern unsigned long _find_next_bit(const unsigned long *addr1,
> >  		const unsigned long *addr2, unsigned long nbits,
> >  		unsigned long start, unsigned long invert, unsigned long le);
> > +extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
> > +extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
> > +extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);
> >  
> >  #ifndef find_next_bit
> >  /**
> > @@ -102,8 +105,17 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
> >   * Returns the bit number of the first set bit.
> >   * If no bits are set, returns @size.
> >   */
> > -extern unsigned long find_first_bit(const unsigned long *addr,
> > -				    unsigned long size);
> > +static inline
> > +unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
> > +{
> > +	if (small_const_nbits(size)) {
> > +		unsigned long val = *addr & BITS_FIRST(size - 1);
> > +
> > +		return val ? __ffs(val) : size;
> 
> This patch results in:
> 
> include/asm-generic/bitops/find.h: In function 'find_last_bit':
> include/asm-generic/bitops/find.h:164:16: error: implicit declaration of function '__fls'; did you mean '__ffs'?
> 
> and:
> 
> ./include/asm-generic/bitops/__fls.h: At top level:
> ./include/asm-generic/bitops/__fls.h:13:38: error: conflicting types for '__fls'
> 
> when building scripts/mod/devicetable-offsets.o.
> 
> Seen with h8300 builds.
> 
> Guenter

The patch is here:

https://lkml.org/lkml/2021/4/1/1184

Yury