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Message-ID: <20230322184335.558195206@goodmis.org>
Date: Wed, 22 Mar 2023 14:42:49 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Uros Bizjak <ubizjak@...il.com>,
Mukesh Ojha <quic_mojha@...cinc.com>
Subject: [for-next][PATCH 10/11] ring_buffer: Use try_cmpxchg instead of cmpxchg
From: Uros Bizjak <ubizjak@...il.com>
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@...nel.org>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Acked-by: Mukesh Ojha <quic_mojha@...cinc.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
kernel/trace/ring_buffer.c | 8 ++++----
1 file 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);
--
2.39.1
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