Commit 153368ce authored Mar 17, 2020 by Steven Rostedt (VMware)

ring-buffer: Optimize rb_iter_head_event()

As it is fine to perform several "peeks" of event data in the ring buffer
via the iterator before moving it forward, do not re-read the event, just
return what was read before. Otherwise, it can cause inconsistent results,
especially when testing multiple CPU buffers to interleave them.

Link: http://lkml.kernel.org/r/20200317213416.592032170@goodmis.org

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent ff84c50c

kernel/trace/ring_buffer.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1929,6 +1929,9 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
		unsigned long commit;
		unsigned length;

		if (iter->head != iter->next_event)
		return iter->event;

		/*
		* When the writer goes across pages, it issues a cmpxchg which
		* is a mb(), which will synchronize with the rmb here.

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