From 8328e36da9cd8cb051394630e910cbb461f7e3ec Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Sun, 5 Mar 2023 16:55:32 +0100 Subject: 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 Signed-off-by: Uros Bizjak Acked-by: Mukesh Ojha Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'kernel/trace') 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); -- cgit v1.2.3