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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 /lib/find_bit.c
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 'lib/find_bit.c')
-rw-r--r--lib/find_bit.c119
1 files changed, 70 insertions, 49 deletions
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 61ec2992938b..d00ee23ab657 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -40,57 +40,33 @@
sz; \
})
-#if !defined(find_next_bit) || !defined(find_next_zero_bit) || \
- !defined(find_next_bit_le) || !defined(find_next_zero_bit_le) || \
- !defined(find_next_and_bit)
/*
- * This is a common helper function for find_next_bit, find_next_zero_bit, and
- * find_next_and_bit. The differences are:
- * - The "invert" argument, which is XORed with each fetched word before
- * searching it for one bits.
- * - The optional "addr2", which is anded with "addr1" if present.
+ * Common helper for find_next_bit() function family
+ * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
+ * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
+ * @size: The bitmap size in bits
+ * @start: The bitnumber to start searching at
*/
-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 tmp, mask;
-
- if (unlikely(start >= nbits))
- return nbits;
-
- tmp = addr1[start / BITS_PER_LONG];
- if (addr2)
- tmp &= addr2[start / BITS_PER_LONG];
- tmp ^= invert;
-
- /* Handle 1st word. */
- mask = BITMAP_FIRST_WORD_MASK(start);
- if (le)
- mask = swab(mask);
-
- tmp &= mask;
-
- start = round_down(start, BITS_PER_LONG);
-
- while (!tmp) {
- start += BITS_PER_LONG;
- if (start >= nbits)
- return nbits;
-
- tmp = addr1[start / BITS_PER_LONG];
- if (addr2)
- tmp &= addr2[start / BITS_PER_LONG];
- tmp ^= invert;
- }
-
- if (le)
- tmp = swab(tmp);
-
- return min(start + __ffs(tmp), nbits);
-}
-EXPORT_SYMBOL(_find_next_bit);
-#endif
+#define FIND_NEXT_BIT(FETCH, MUNGE, size, start) \
+({ \
+ unsigned long mask, idx, tmp, sz = (size), __start = (start); \
+ \
+ if (unlikely(__start >= sz)) \
+ goto out; \
+ \
+ mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start)); \
+ idx = __start / BITS_PER_LONG; \
+ \
+ for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) { \
+ if ((idx + 1) * BITS_PER_LONG >= sz) \
+ goto out; \
+ idx++; \
+ } \
+ \
+ sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz); \
+out: \
+ sz; \
+})
#ifndef find_first_bit
/*
@@ -127,6 +103,32 @@ unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size
EXPORT_SYMBOL(_find_first_zero_bit);
#endif
+#ifndef find_next_bit
+unsigned long _find_next_bit(const unsigned long *addr, unsigned long nbits, unsigned long start)
+{
+ return FIND_NEXT_BIT(addr[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_bit);
+#endif
+
+#ifndef find_next_and_bit
+unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long *addr2,
+ unsigned long nbits, unsigned long start)
+{
+ return FIND_NEXT_BIT(addr1[idx] & addr2[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_and_bit);
+#endif
+
+#ifndef find_next_zero_bit
+unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
+ unsigned long start)
+{
+ return FIND_NEXT_BIT(~addr[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_zero_bit);
+#endif
+
#ifndef find_last_bit
unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
{
@@ -175,4 +177,23 @@ EXPORT_SYMBOL(_find_first_zero_bit_le);
#endif
+#ifndef find_next_zero_bit_le
+unsigned long _find_next_zero_bit_le(const unsigned long *addr,
+ unsigned long size, unsigned long offset)
+{
+ return FIND_NEXT_BIT(~addr[idx], swab, size, offset);
+}
+EXPORT_SYMBOL(_find_next_zero_bit_le);
+#endif
+
+#ifndef find_next_bit_le
+unsigned long _find_next_bit_le(const unsigned long *addr,
+ unsigned long size, unsigned long offset)
+{
+ return FIND_NEXT_BIT(addr[idx], swab, size, offset);
+}
+EXPORT_SYMBOL(_find_next_bit_le);
+
+#endif
+
#endif /* __BIG_ENDIAN */