From 6cc18331a987c4a29d66b9c4fd292587fba4d7bd Mon Sep 17 00:00:00 2001 From: Yury Norov Date: Mon, 19 Sep 2022 14:05:56 -0700 Subject: [PATCH] lib/find_bit: add find_next{,_and}_bit_wrap The helper is better optimized for the worst case: in case of empty cpumask, current code traverses 2 * size: next = cpumask_next_and(prev, src1p, src2p); if (next >= nr_cpu_ids) next = cpumask_first_and(src1p, src2p); At bitmap level we can stop earlier after checking 'size + offset' bits. Signed-off-by: Yury Norov --- include/linux/find.h | 46 ++++++++++++++++++++++++++++++++++++++++++++ lib/cpumask.c | 12 +++--------- 2 files changed, 49 insertions(+), 9 deletions(-) diff --git a/include/linux/find.h b/include/linux/find.h index 128615a3f93e..77c087b7a451 100644 --- a/include/linux/find.h +++ b/include/linux/find.h @@ -290,6 +290,52 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size) } #endif +/** + * find_next_and_bit_wrap - find the next set bit in both memory regions + * @addr1: The first address to base the search on + * @addr2: The second address to base the search on + * @size: The bitmap size in bits + * @offset: The bitnumber to start searching at + * + * Returns the bit number for the next set bit, or first set bit up to @offset + * If no bits are set, returns @size. + */ +static inline +unsigned long find_next_and_bit_wrap(const unsigned long *addr1, + const unsigned long *addr2, + unsigned long size, unsigned long offset) +{ + unsigned long bit = find_next_and_bit(addr1, addr2, size, offset); + + if (bit < size) + return bit; + + bit = find_first_and_bit(addr1, addr2, offset); + return bit < offset ? bit : size; +} + +/** + * find_next_bit_wrap - find the next set bit in both memory regions + * @addr: The first address to base the search on + * @size: The bitmap size in bits + * @offset: The bitnumber to start searching at + * + * Returns the bit number for the next set bit, or first set bit up to @offset + * If no bits are set, returns @size. + */ +static inline +unsigned long find_next_bit_wrap(const unsigned long *addr, + unsigned long size, unsigned long offset) +{ + unsigned long bit = find_next_bit(addr, size, offset); + + if (bit < size) + return bit; + + bit = find_first_bit(addr, offset); + return bit < offset ? bit : size; +} + /** * find_next_clump8 - find next 8-bit clump with set bits in a memory region * @clump: location to store copy of found clump diff --git a/lib/cpumask.c b/lib/cpumask.c index 2c4a63b6f03f..c7c392514fd3 100644 --- a/lib/cpumask.c +++ b/lib/cpumask.c @@ -166,10 +166,8 @@ unsigned int cpumask_any_and_distribute(const struct cpumask *src1p, /* NOTE: our first selection will skip 0. */ prev = __this_cpu_read(distribute_cpu_mask_prev); - next = cpumask_next_and(prev, src1p, src2p); - if (next >= nr_cpu_ids) - next = cpumask_first_and(src1p, src2p); - + next = find_next_and_bit_wrap(cpumask_bits(src1p), cpumask_bits(src2p), + nr_cpumask_bits, prev + 1); if (next < nr_cpu_ids) __this_cpu_write(distribute_cpu_mask_prev, next); @@ -183,11 +181,7 @@ unsigned int cpumask_any_distribute(const struct cpumask *srcp) /* NOTE: our first selection will skip 0. */ prev = __this_cpu_read(distribute_cpu_mask_prev); - - next = cpumask_next(prev, srcp); - if (next >= nr_cpu_ids) - next = cpumask_first(srcp); - + next = find_next_bit_wrap(cpumask_bits(srcp), nr_cpumask_bits, prev + 1); if (next < nr_cpu_ids) __this_cpu_write(distribute_cpu_mask_prev, next); -- 2.25.1