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/20230305155532.5549-4-ubizjak@gmail.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 93f854433d89be9b58b3acafb25b075561f41f44..2d5c3caff32d72a5d14908877285be58954b9b68 100644 (file)
--- 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);