linux/arch
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
..
alpha Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mattst88/alpha 2018-02-02 13:46:21 -08:00
arc The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
arm lib: optimize cpumask_next_and() 2018-02-06 18:32:44 -08:00
arm64 bitmap: replace bitmap_{from,to}_u32array 2018-02-06 18:32:44 -08:00
blackfin The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
c6x The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
cris The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
frv The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
h8300 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
hexagon The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
ia64 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
m32r The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
m68k lib: optimize cpumask_next_and() 2018-02-06 18:32:44 -08:00
metag The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
microblaze Microblaze patches for 4.16-rc1 2018-02-02 09:48:36 -08:00
mips The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
mn10300 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
nios2 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
openrisc The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
parisc The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
powerpc powerpc updates for 4.16 2018-02-02 10:01:04 -08:00
riscv The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
s390 The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
score The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
sh The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
sparc The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
tile The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
um The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
unicore32 lib: optimize cpumask_next_and() 2018-02-06 18:32:44 -08:00
x86 Makefile: move stack-protector availability out of Kconfig 2018-02-06 18:32:44 -08:00
xtensa The core framework has a handful of patches this time around, mostly due 2018-02-01 16:56:07 -08:00
.gitignore
Kconfig Makefile: introduce CONFIG_CC_STACKPROTECTOR_AUTO 2018-02-06 18:32:44 -08:00