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ring_buffer: Use try_cmpxchg instead of cmpxchg

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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>
This commit is contained in:
Uros Bizjak 2023-07-14 17:43:34 +02:00 committed by Steven Rostedt (Google)
parent e7186af7fb
commit 00a8478f8f
1 changed files with 6 additions and 14 deletions
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20
kernel/trace/ring_buffer.c
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@ -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;