Commit 8328e36d authored by Uros Bizjak's avatar Uros Bizjak Committed by Steven Rostedt (Google)
Browse files

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: default avatarUros Bizjak <ubizjak@gmail.com>
Acked-by: default avatarMukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent bc92b956

kernel/trace/ring_buffer.c

+4 −4
Original line number Diff line number Diff line
@@ -4057,10 +4057,10 @@ void ring_buffer_record_off(struct trace_buffer *buffer) 
	unsigned int rd;

	unsigned int new_rd;



	do {

	rd = atomic_read(&buffer->record_disabled);

	do {

		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;



	do {

	rd = atomic_read(&buffer->record_disabled);

	do {

		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);