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ring_buffer: Use try_cmpxchg instead of cmpxchg

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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>
This commit is contained in:
Uros Bizjak 2023-03-05 16:55:32 +01:00 committed by Steven Rostedt (Google)
parent bc92b9562a
commit 8328e36da9
1 changed files with 4 additions and 4 deletions
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8
kernel/trace/ring_buffer.c
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@ -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);