ring_buffer: Use try_cmpxchg instead of cmpxchg

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old.
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. There is no need to re-read the value in the loop.

No functional change intended.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Masami Hiramatsu <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
Acked-by: Mukesh Ojha <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 93f854433d89..2d5c3caff32d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4057,10 +4057,10 @@ void ring_buffer_record_off(struct trace_buffer *buffer)
 	unsigned int rd;
 	unsigned int new_rd;
 
+	rd = atomic_read(&buffer->record_disabled);
 	do {
-		rd = atomic_read(&buffer->record_disabled);
 		new_rd = rd | RB_BUFFER_OFF;
-	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
+	} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_off);
 
@@ -4080,10 +4080,10 @@ void ring_buffer_record_on(struct trace_buffer *buffer)
 	unsigned int rd;
 	unsigned int new_rd;
 
+	rd = atomic_read(&buffer->record_disabled);
 	do {
-		rd = atomic_read(&buffer->record_disabled);
 		new_rd = rd & ~RB_BUFFER_OFF;
-	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
+	} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
 }
 EXPORT_SYMBOL_GPL(ring_buffer_record_on);