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authorYury Norov <yury.norov@gmail.com>2022-09-14 19:07:29 -0700
committerYury Norov <yury.norov@gmail.com>2022-09-21 12:21:32 -0700
commite79864f3164c573afce09ec4b72b75ebe061c14d (patch)
tree56ab7f1d70fec5d7005493c512ff221c3a4e29f1 /include/linux/find.h
parent14a99e130f2758bc826a7e7a8bdf6f7400b54f0f (diff)
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>
Diffstat (limited to 'include/linux/find.h')
-rw-r--r--include/linux/find.h23
1 files changed, 15 insertions, 8 deletions
diff --git a/include/linux/find.h b/include/linux/find.h
index 2464bff5de04..dead6f53a97b 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -8,9 +8,12 @@
#include <linux/bitops.h>
-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);
+unsigned long _find_next_bit(const unsigned long *addr1, unsigned long nbits,
+ unsigned long start);
+unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long *addr2,
+ unsigned long nbits, unsigned long start);
+unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
+ unsigned long start);
extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
extern unsigned long _find_first_and_bit(const unsigned long *addr1,
const unsigned long *addr2, unsigned long size);
@@ -19,6 +22,10 @@ extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long siz
#ifdef __BIG_ENDIAN
unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size);
+unsigned long _find_next_zero_bit_le(const unsigned long *addr, unsigned
+ long size, unsigned long offset);
+unsigned long _find_next_bit_le(const unsigned long *addr, unsigned
+ long size, unsigned long offset);
#endif
#ifndef find_next_bit
@@ -45,7 +52,7 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
return val ? __ffs(val) : size;
}
- return _find_next_bit(addr, NULL, size, offset, 0UL, 0);
+ return _find_next_bit(addr, size, offset);
}
#endif
@@ -75,7 +82,7 @@ unsigned long find_next_and_bit(const unsigned long *addr1,
return val ? __ffs(val) : size;
}
- return _find_next_bit(addr1, addr2, size, offset, 0UL, 0);
+ return _find_next_and_bit(addr1, addr2, size, offset);
}
#endif
@@ -103,7 +110,7 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
return val == ~0UL ? size : ffz(val);
}
- return _find_next_bit(addr, NULL, size, offset, ~0UL, 0);
+ return _find_next_zero_bit(addr, size, offset);
}
#endif
@@ -251,7 +258,7 @@ unsigned long find_next_zero_bit_le(const void *addr, unsigned
return val == ~0UL ? size : ffz(val);
}
- return _find_next_bit(addr, NULL, size, offset, ~0UL, 1);
+ return _find_next_zero_bit_le(addr, size, offset);
}
#endif
@@ -284,7 +291,7 @@ unsigned long find_next_bit_le(const void *addr, unsigned
return val ? __ffs(val) : size;
}
- return _find_next_bit(addr, NULL, size, offset, 0UL, 1);
+ return _find_next_bit_le(addr, size, offset);
}
#endif