Commit Graph

18 Commits

Author SHA1 Message Date
Valentin Schneider 90d482908e lib/find_bit: Introduce find_next_andnot_bit()
In preparation of introducing for_each_cpu_andnot(), add a variant of
find_next_bit() that negate the bits in @addr2 when ANDing them with the
bits in @addr1.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
2022-10-06 05:57:36 -07:00
Yury Norov 3cea8d4753 lib: add find_nth{,_and,_andnot}_bit()
Kernel lacks for a function that searches for Nth bit in a bitmap.
Usually people do it like this:
	for_each_set_bit(bit, mask, size)
		if (n-- == 0)
			return bit;

We can do it more efficiently, if we:
1. find a word containing Nth bit, using hweight(); and
2. find the bit, using a helper fns(), that works similarly to
   __ffs() and ffz().

fns() is implemented as a simple loop. For x86_64, there's PDEP instruction
to do that: ret = clz(pdep(1 << idx, num)). However, for large bitmaps the
most of improvement comes from using hweight(), so I kept fns() simple.

New find_nth_bit() is ~70 times faster on x86_64/kvm in find_bit benchmark:
find_nth_bit:                  7154190 ns,  16411 iterations
for_each_bit:                505493126 ns,  16315 iterations

With all that, a family of 3 new functions is added, and used where
appropriate in the following patches.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
2022-09-26 12:19:12 -07:00
Yury Norov e79864f316 lib/find_bit: optimize find_next_bit() functions
Over the past couple years, the function _find_next_bit() was extended
with parameters that modify its behavior to implement and- zero- and le-
flavors. The parameters are passed at compile time, but current design
prevents a compiler from optimizing out the conditionals.

As find_next_bit() API grows, I expect that more parameters will be added.
Current design would require more conditional code in _find_next_bit(),
which would bloat the helper even more and make it barely readable.

This patch replaces _find_next_bit() with a macro FIND_NEXT_BIT, and adds
a set of wrappers, so that the compile-time optimizations become possible.

The common logic is moved to the new macro, and all flavors may be
generated by providing a FETCH macro parameter, like in this example:

  #define FIND_NEXT_BIT(FETCH, MUNGE, size, start) ...

  find_next_xornot_and_bit(addr1, addr2, addr3, size, start)
  {
	return FIND_NEXT_BIT(addr1[idx] ^ ~addr2[idx] & addr3[idx],
				/* nop */, size, start);
  }

The FETCH may be of any complexity, as soon as it only refers the bitmap(s)
and an iterator idx.

MUNGE is here to support _le code generation for BE builds. May be
empty.

I ran find_bit_benchmark 16 times on top of 6.0-rc2 and 16 times on top
of 6.0-rc2 + this series. The results for kvm/x86_64 are:

                      v6.0-rc2  Optimized       Difference  Z-score
Random dense bitmap         ns         ns        ns      %
find_next_bit:          787735     670546    117189   14.9     3.97
find_next_zero_bit:     777492     664208    113284   14.6    10.51
find_last_bit:          830925     687573    143352   17.3     2.35
find_first_bit:        3874366    3306635    567731   14.7     1.84
find_first_and_bit:   40677125   37739887   2937238    7.2     1.36
find_next_and_bit:      347865     304456     43409   12.5     1.35

Random sparse bitmap
find_next_bit:           19816      14021      5795   29.2     6.10
find_next_zero_bit:    1318901    1223794     95107    7.2     1.41
find_last_bit:           14573      13514      1059    7.3     6.92
find_first_bit:        1313321    1249024     64297    4.9     1.53
find_first_and_bit:       8921       8098       823    9.2     4.56
find_next_and_bit:        9796       7176      2620   26.7     5.39

Where the statistics is significant (z-score > 3), the improvement
is ~15%.

According to the bloat-o-meter, the Image size is 10-11K less:

x86_64/defconfig:
add/remove: 32/14 grow/shrink: 61/782 up/down: 6344/-16521 (-10177)

arm64/defconfig:
add/remove: 3/2 grow/shrink: 50/714 up/down: 608/-11556 (-10948)

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
2022-09-21 12:21:32 -07:00
Yury Norov 14a99e130f lib/find_bit: create find_first_zero_bit_le()
find_first_zero_bit_le() is an alias to find_next_zero_bit_le(),
despite that 'next' is known to be slower than 'first' version.

Now that we have common FIND_FIRST_BIT() macro helper, it's trivial
to implement find_first_zero_bit_le() as a real function.

Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
2022-09-21 12:17:18 -07:00
Yury Norov 58414bbb58 lib/find_bit: introduce FIND_FIRST_BIT() macro
Now that we have many flavors of find_first_bit(), and expect even more,
it's better to have one macro that generates optimal code for all and makes
maintaining of slightly different functions simpler.

The logic common to all versions is moved to the new macro, and all the
flavors are generated by providing an FETCH macro-parameter, like
in this example:

  #define FIND_FIRST_BIT(FETCH, MUNGE, size) ...

  find_first_ornot_and_bit(addr1, addr2, addr3, size)
  {
        return FIND_FIRST_BIT(addr1[idx] | ~addr2[idx] & addr3[idx], /* nop */, size);
  }

The FETCH may be of any complexity, as soon as it only refers
the bitmap(s) and an iterator idx.

MUNGE is here to support _le code generation for BE builds. May be
empty.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
2022-09-21 12:15:53 -07:00
Yury Norov f68edc9297 lib: add find_first_and_bit()
Currently find_first_and_bit() is an alias to find_next_and_bit(). However,
it is widely used in cpumask, so it worth to optimize it. This patch adds
its own implementation for find_first_and_bit().

On x86_64 find_bit_benchmark says:

Before (#define find_first_and_bit(...) find_next_and_bit(..., 0):
Start testing find_bit() with random-filled bitmap
[  140.291468] find_first_and_bit:           46890919 ns,  32671 iterations
Start testing find_bit() with sparse bitmap
[  140.295028] find_first_and_bit:               7103 ns,      1 iterations

After:
Start testing find_bit() with random-filled bitmap
[  162.574907] find_first_and_bit:           25045813 ns,  32846 iterations
Start testing find_bit() with sparse bitmap
[  162.578458] find_first_and_bit:               4900 ns,      1 iterations

(Thanks to Alexey Klimov for thorough testing.)

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Alexey Klimov <aklimov@redhat.com>
2022-01-15 08:47:31 -08:00
Yury Norov 2cc7b6a44a lib: add fast path for find_first_*_bit() and find_last_bit()
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.

Link: https://lkml.kernel.org/r/20210401003153.97325-11-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Alexey Klimov <aklimov@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jianpeng Ma <jianpeng.ma@intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Yoshinori Sato <ysato@users.osdn.me>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-06 19:24:12 -07:00
Yury Norov 5c88af59f9 lib: inline _find_next_bit() wrappers
lib/find_bit.c declares five single-line wrappers for _find_next_bit().
We may turn those wrappers to inline functions.  It eliminates unneeded
function calls and opens room for compile-time optimizations.

Link: https://lkml.kernel.org/r/20210401003153.97325-8-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Alexey Klimov <aklimov@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jianpeng Ma <jianpeng.ma@intel.com>
Cc: Joe Perches <joe@perches.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Yoshinori Sato <ysato@users.osdn.me>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-06 19:24:12 -07:00
Andy Shevchenko aa6159ab99 kernel.h: split out mathematical helpers
kernel.h is being used as a dump for all kinds of stuff for a long time.
Here is the attempt to start cleaning it up by splitting out
mathematical helpers.

At the same time convert users in header and lib folder to use new
header.  Though for time being include new header back to kernel.h to
avoid twisted indirected includes for existing users.

[sfr@canb.auug.org.au: fix powerpc build]
  Link: https://lkml.kernel.org/r/20201029150809.13059608@canb.auug.org.au

Link: https://lkml.kernel.org/r/20201028173212.41768-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 22:46:15 -08:00
Andy Shevchenko b296a6d533 kernel.h: split out min()/max() et al. helpers
kernel.h is being used as a dump for all kinds of stuff for a long time.
Here is the attempt to start cleaning it up by splitting out min()/max()
et al.  helpers.

At the same time convert users in header and lib folder to use new header.
Though for time being include new header back to kernel.h to avoid
twisted indirected includes for other existing users.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Joe Perches <joe@perches.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200910164152.GA1891694@smile.fi.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:11:19 -07:00
Yury Norov 7dfaa98f64 lib/find_bit.c: uninline helper _find_next_bit()
It saves 25% of .text for arm64, and more for BE architectures.

Before:
  $ size lib/find_bit.o
     text    data     bss     dec     hex filename
     1012      56       0    1068     42c lib/find_bit.o

After:
  $ size lib/find_bit.o
     text    data     bss     dec     hex filename
      776      56       0     832     340 lib/find_bit.o

Link: http://lkml.kernel.org/r/20200103202846.21616-3-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Allison Randal <allison@lohutok.net>
Cc: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 10:30:41 -08:00
Yury Norov b78c57135d lib/find_bit.c: join _find_next_bit{_le}
_find_next_bit and _find_next_bit_le are very similar functions.  It's
possible to join them by adding 1 parameter and a couple of simple
checks.  It's simplify maintenance and make possible to shrink the size
of .text by un-inlining the unified function (in the following patch).

Link: http://lkml.kernel.org/r/20200103202846.21616-2-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Joe Perches <joe@perches.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 10:30:40 -08:00
Yury Norov d5767057c9 uapi: rename ext2_swab() to swab() and share globally in swab.h
ext2_swab() is defined locally in lib/find_bit.c However it is not
specific to ext2, neither to bitmaps.

There are many potential users of it, so rename it to just swab() and
move to include/uapi/linux/swab.h

ABI guarantees that size of unsigned long corresponds to BITS_PER_LONG,
therefore drop unneeded cast.

Link: http://lkml.kernel.org/r/20200103202846.21616-1-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Joe Perches <joe@perches.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 10:30:40 -08:00
William Breathitt Gray 169c474fb2 bitops: introduce the for_each_set_clump8 macro
Pach series "Introduce the for_each_set_clump8 macro", v18.

While adding GPIO get_multiple/set_multiple callback support for various
drivers, I noticed a pattern of looping manifesting that would be useful
standardized as a macro.

This patchset introduces the for_each_set_clump8 macro and utilizes it
in several GPIO drivers.  The for_each_set_clump macro8 facilitates a
for-loop syntax that iterates over a memory region entire groups of set
bits at a time.

For example, suppose you would like to iterate over a 32-bit integer 8
bits at a time, skipping over 8-bit groups with no set bit, where
XXXXXXXX represents the current 8-bit group:

    Example:        10111110 00000000 11111111 00110011
    First loop:     10111110 00000000 11111111 XXXXXXXX
    Second loop:    10111110 00000000 XXXXXXXX 00110011
    Third loop:     XXXXXXXX 00000000 11111111 00110011

Each iteration of the loop returns the next 8-bit group that has at
least one set bit.

The for_each_set_clump8 macro has four parameters:

    * start: set to the bit offset of the current clump
    * clump: set to the current clump value
    * bits: bitmap to search within
    * size: bitmap size in number of bits

In this version of the patchset, the for_each_set_clump macro has been
reimplemented and simplified based on the suggestions provided by Rasmus
Villemoes and Andy Shevchenko in the version 4 submission.

In particular, the function of the for_each_set_clump macro has been
restricted to handle only 8-bit clumps; the drivers that use the
for_each_set_clump macro only handle 8-bit ports so a generic
for_each_set_clump implementation is not necessary.  Thus, a solution
for large clumps (i.e.  those larger than the width of a bitmap word)
can be postponed until a driver appears that actually requires such a
generic for_each_set_clump implementation.

For what it's worth, a semi-generic for_each_set_clump (i.e.  for clumps
smaller than the width of a bitmap word) can be implemented by simply
replacing the hardcoded '8' and '0xFF' instances with respective
variables.  I have not yet had a need for such an implementation, and
since it falls short of a true generic for_each_set_clump function, I
have decided to forgo such an implementation for now.

In addition, the bitmap_get_value8 and bitmap_set_value8 functions are
introduced to get and set 8-bit values respectively.  Their use is based
on the behavior suggested in the patchset version 4 review.

This patch (of 14):

This macro iterates for each 8-bit group of bits (clump) with set bits,
within a bitmap memory region.  For each iteration, "start" is set to
the bit offset of the found clump, while the respective clump value is
stored to the location pointed by "clump".  Additionally, the
bitmap_get_value8 and bitmap_set_value8 functions are introduced to
respectively get and set an 8-bit value in a bitmap memory region.

[gustavo@embeddedor.com: fix potential sign-extension overflow]
  Link: http://lkml.kernel.org/r/20191015184657.GA26541@embeddedor
[akpm@linux-foundation.org: s/ULL/UL/, per Joe]
[vilhelm.gray@gmail.com: add for_each_set_clump8 documentation]
  Link: http://lkml.kernel.org/r/20191016161825.301082-1-vilhelm.gray@gmail.com
Link: http://lkml.kernel.org/r/893c3b4f03266c9496137cc98ac2b1bd27f92c73.1570641097.git.vilhelm.gray@gmail.com
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Suggested-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Phil Reid <preid@electromag.com.au>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Cc: Morten Hein Tiljeset <morten.tiljeset@prevas.dk>
Cc: Sean Nyekjaer <sean.nyekjaer@prevas.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-04 19:44:12 -08:00
Thomas Gleixner 2874c5fd28 treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152
Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license as published by
  the free software foundation either version 2 of the license or at
  your option any later version

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-30 11:26:32 -07:00
Clement Courbet 0ade34c370 lib: optimize cpumask_next_and()
We've measured that we spend ~0.6% of sys cpu time in cpumask_next_and().
It's essentially a joined iteration in search for a non-zero bit, which is
currently implemented as a lookup join (find a nonzero bit on the lhs,
lookup the rhs to see if it's set there).

Implement a direct join (find a nonzero bit on the incrementally built
join).  Also add generic bitmap benchmarks in the new `test_find_bit`
module for new function (see `find_next_and_bit` in [2] and [3] below).

For cpumask_next_and, direct benchmarking shows that it's 1.17x to 14x
faster with a geometric mean of 2.1 on 32 CPUs [1].  No impact on memory
usage.  Note that on Arm, the new pure-C implementation still outperforms
the old one that uses a mix of C and asm (`find_next_bit`) [3].

[1] Approximate benchmark code:

```
  unsigned long src1p[nr_cpumask_longs] = {pattern1};
  unsigned long src2p[nr_cpumask_longs] = {pattern2};
  for (/*a bunch of repetitions*/) {
    for (int n = -1; n <= nr_cpu_ids; ++n) {
      asm volatile("" : "+rm"(src1p)); // prevent any optimization
      asm volatile("" : "+rm"(src2p));
      unsigned long result = cpumask_next_and(n, src1p, src2p);
      asm volatile("" : "+rm"(result));
    }
  }
```

Results:
pattern1    pattern2     time_before/time_after
0x0000ffff  0x0000ffff   1.65
0x0000ffff  0x00005555   2.24
0x0000ffff  0x00001111   2.94
0x0000ffff  0x00000000   14.0
0x00005555  0x0000ffff   1.67
0x00005555  0x00005555   1.71
0x00005555  0x00001111   1.90
0x00005555  0x00000000   6.58
0x00001111  0x0000ffff   1.46
0x00001111  0x00005555   1.49
0x00001111  0x00001111   1.45
0x00001111  0x00000000   3.10
0x00000000  0x0000ffff   1.18
0x00000000  0x00005555   1.18
0x00000000  0x00001111   1.17
0x00000000  0x00000000   1.25
-----------------------------
               geo.mean  2.06

[2] test_find_next_bit, X86 (skylake)

 [ 3913.477422] Start testing find_bit() with random-filled bitmap
 [ 3913.477847] find_next_bit: 160868 cycles, 16484 iterations
 [ 3913.477933] find_next_zero_bit: 169542 cycles, 16285 iterations
 [ 3913.478036] find_last_bit: 201638 cycles, 16483 iterations
 [ 3913.480214] find_first_bit: 4353244 cycles, 16484 iterations
 [ 3913.480216] Start testing find_next_and_bit() with random-filled
 bitmap
 [ 3913.481074] find_next_and_bit: 89604 cycles, 8216 iterations
 [ 3913.481075] Start testing find_bit() with sparse bitmap
 [ 3913.481078] find_next_bit: 2536 cycles, 66 iterations
 [ 3913.481252] find_next_zero_bit: 344404 cycles, 32703 iterations
 [ 3913.481255] find_last_bit: 2006 cycles, 66 iterations
 [ 3913.481265] find_first_bit: 17488 cycles, 66 iterations
 [ 3913.481266] Start testing find_next_and_bit() with sparse bitmap
 [ 3913.481272] find_next_and_bit: 764 cycles, 1 iterations

[3] test_find_next_bit, arm (v7 odroid XU3).

[  267.206928] Start testing find_bit() with random-filled bitmap
[  267.214752] find_next_bit: 4474 cycles, 16419 iterations
[  267.221850] find_next_zero_bit: 5976 cycles, 16350 iterations
[  267.229294] find_last_bit: 4209 cycles, 16419 iterations
[  267.279131] find_first_bit: 1032991 cycles, 16420 iterations
[  267.286265] Start testing find_next_and_bit() with random-filled
bitmap
[  267.302386] find_next_and_bit: 2290 cycles, 8140 iterations
[  267.309422] Start testing find_bit() with sparse bitmap
[  267.316054] find_next_bit: 191 cycles, 66 iterations
[  267.322726] find_next_zero_bit: 8758 cycles, 32703 iterations
[  267.329803] find_last_bit: 84 cycles, 66 iterations
[  267.336169] find_first_bit: 4118 cycles, 66 iterations
[  267.342627] Start testing find_next_and_bit() with sparse bitmap
[  267.356919] find_next_and_bit: 91 cycles, 1 iterations

[courbet@google.com: v6]
  Link: http://lkml.kernel.org/r/20171129095715.23430-1-courbet@google.com
[geert@linux-m68k.org: m68k/bitops: always include <asm-generic/bitops/find.h>]
  Link: http://lkml.kernel.org/r/1512556816-28627-1-git-send-email-geert@linux-m68k.org
Link: http://lkml.kernel.org/r/20171128131334.23491-1-courbet@google.com
Signed-off-by: Clement Courbet <courbet@google.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Yury Norov <ynorov@caviumnetworks.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-02-06 18:32:44 -08:00
Matthew Wilcox e4afd2e556 lib/find_bit.c: micro-optimise find_next_*_bit
This saves 32 bytes on my x86-64 build, mostly due to alignment
considerations and sharing more code between find_next_bit and
find_next_zero_bit, but it does save a couple of instructions.

There's really two parts to this commit:
 - First, the first half of the test: (!nbits || start >= nbits) is
   trivially a subset of the second half, since nbits and start are both
   unsigned
 - Second, while looking at the disassembly, I noticed that GCC was
   predicting the branch taken. Since this is a failure case, it's
   clearly the less likely of the two branches, so add an unlikely() to
   override GCC's heuristics.

[mawilcox@microsoft.com: v2]
  Link: http://lkml.kernel.org/r/1483709016-1834-1-git-send-email-mawilcox@linuxonhyperv.com
Link: http://lkml.kernel.org/r/1483709016-1834-1-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Yury Norov <ynorov@caviumnetworks.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24 17:46:57 -08:00
Yury Norov 840620a159 lib: rename lib/find_next_bit.c to lib/find_bit.c
This file contains implementation for all find_*_bit{,_le}
So giving it more generic name looks reasonable.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: George Spelvin <linux@horizon.com>
Cc: Alexey Klimov <klimov.linux@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Valentin Rothberg <valentinrothberg@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-04-17 09:03:54 -04:00