| Message ID | 20230305155532.5549-4-ubizjak@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 8328e36da9cd8cb051394630e910cbb461f7e3ec |
| Headers | show |
| Series | Improve trace/ring_buffer.c | expand |
On 3/5/2023 9:25 PM, Uros Bizjak wrote: > 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. > > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com> > --- > v2: Convert only loops with cmpxchg. > --- > 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 5235037f83d3..d17345b522f4 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -4061,10 +4061,10 @@ 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); > > @@ -4084,10 +4084,10 @@ 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)); > } Acked-by: Mukesh Ojha <quic_mojha@quicinc.com> -Mukesh > EXPORT_SYMBOL_GPL(ring_buffer_record_on); >
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 5235037f83d3..d17345b522f4 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4061,10 +4061,10 @@ 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); @@ -4084,10 +4084,10 @@ 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);
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. Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- v2: Convert only loops with cmpxchg. --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)