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| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-14 17:43:34 +0200 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-07-30 18:11:45 -0400 |
| commit | 00a8478f8f5c0201004240746dd74d69d86fc0c4 (patch) | |
| tree | 823215d91b6a2243e1fd5c8a8bf721c541a8c117 /kernel/trace | |
| parent | e7186af7fb2609584a8bfb3da3c6ae09da5a5224 (diff) | |
| download | linux-stable-00a8478f8f5c0201004240746dd74d69d86fc0c4.tar.gz linux-stable-00a8478f8f5c0201004240746dd74d69d86fc0c4.tar.bz2 linux-stable-00a8478f8f5c0201004240746dd74d69d86fc0c4.zip | |
ring_buffer: Use try_cmpxchg instead of cmpxchg
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
ring_buffer.c. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
No functional change intended.
Link: https://lore.kernel.org/linux-trace-kernel/20230714154418.8884-1-ubizjak@gmail.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 20 |
1 files changed, 6 insertions, 14 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 52dea5dd5362..78502d4c7214 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -692,10 +692,7 @@ static void rb_time_set(rb_time_t *t, u64 val) static inline bool rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set) { - unsigned long ret; - - ret = local_cmpxchg(l, expect, set); - return ret == expect; + return local_try_cmpxchg(l, &expect, set); } static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set) @@ -752,9 +749,7 @@ static void rb_time_set(rb_time_t *t, u64 val) static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set) { - u64 val; - val = local64_cmpxchg(&t->time, expect, set); - return val == expect; + return local64_try_cmpxchg(&t->time, &expect, set); } #endif @@ -1494,14 +1489,11 @@ static bool rb_head_page_replace(struct buffer_page *old, { unsigned long *ptr = (unsigned long *)&old->list.prev->next; unsigned long val; - unsigned long ret; val = *ptr & ~RB_FLAG_MASK; val |= RB_PAGE_HEAD; - ret = cmpxchg(ptr, val, (unsigned long)&new->list); - - return ret == val; + return try_cmpxchg(ptr, &val, (unsigned long)&new->list); } /* @@ -3003,7 +2995,6 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer, { unsigned long new_index, old_index; struct buffer_page *bpage; - unsigned long index; unsigned long addr; u64 write_stamp; u64 delta; @@ -3060,8 +3051,9 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer, */ old_index += write_mask; new_index += write_mask; - index = local_cmpxchg(&bpage->write, old_index, new_index); - if (index == old_index) { + + /* caution: old_index gets updated on cmpxchg failure */ + if (local_try_cmpxchg(&bpage->write, &old_index, new_index)) { /* update counters */ local_sub(event_length, &cpu_buffer->entries_bytes); return true; |