diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-01-18 16:07:03 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-02-02 22:50:05 -0800 |
| commit | 030c6ff6498881ac842c7f6da5eec181202b29f4 (patch) | |
| tree | f08c6b2f70ed980d645fb671455023fb0e7e59c3 | |
| parent | f3296f80c8065b26a27eb8ab686d0c1d67880524 (diff) | |
lib/genalloc: use try_cmpxchg in {set,clear}_bits_ll
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
{set,clear}_bits_ll. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails.
Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.
The patch also declares these two functions inline, to ensure inlining.
No functional change intended.
Link: https://lkml.kernel.org/r/20230118150703.4024-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | lib/genalloc.c | 18 |
1 files changed, 8 insertions, 10 deletions
diff --git a/lib/genalloc.c b/lib/genalloc.c index 00fc50d0a640..0c883d6fbd44 100644 --- a/lib/genalloc.c +++ b/lib/genalloc.c @@ -40,32 +40,30 @@ static inline size_t chunk_size(const struct gen_pool_chunk *chunk) return chunk->end_addr - chunk->start_addr + 1; } -static int set_bits_ll(unsigned long *addr, unsigned long mask_to_set) +static inline int +set_bits_ll(unsigned long *addr, unsigned long mask_to_set) { - unsigned long val, nval; + unsigned long val = READ_ONCE(*addr); - nval = *addr; do { - val = nval; if (val & mask_to_set) return -EBUSY; cpu_relax(); - } while ((nval = cmpxchg(addr, val, val | mask_to_set)) != val); + } while (!try_cmpxchg(addr, &val, val | mask_to_set)); return 0; } -static int clear_bits_ll(unsigned long *addr, unsigned long mask_to_clear) +static inline int +clear_bits_ll(unsigned long *addr, unsigned long mask_to_clear) { - unsigned long val, nval; + unsigned long val = READ_ONCE(*addr); - nval = *addr; do { - val = nval; if ((val & mask_to_clear) != mask_to_clear) return -EBUSY; cpu_relax(); - } while ((nval = cmpxchg(addr, val, val & ~mask_to_clear)) != val); + } while (!try_cmpxchg(addr, &val, val & ~mask_to_clear)); return 0; } |