Re: [PATCH 1/8] membarrier: Document why membarrier() works

On 6/16/21 12:30 AM, Peter Zijlstra wrote:

On Wed, Jun 16, 2021 at 02:00:37PM +1000, Nicholas Piggin wrote:

quoted

Excerpts from Andy Lutomirski's message of June 16, 2021 1:21 pm:

quoted

We had a nice comment at the top of membarrier.c explaining why membarrier
worked in a handful of scenarios, but that consisted more of a list of
things not to forget than an actual description of the algorithm and why it
should be expected to work.

Add a comment explaining my understanding of the algorithm.  This exposes a
couple of implementation issues that I will hopefully fix up in subsequent
patches.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 kernel/sched/membarrier.c | 55 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index b5add64d9698..3173b063d358 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c

@@ -7,6 +7,61 @@
 #include "sched.h"
 

Precisely describing the orderings is great, not a fan of the style of the
comment though.

I'm with Nick on that; I can't read it :/ It only makes things more
confusing. If you want precision, English (or any natural language) is
your enemy.

To describe ordering use the diagrams and/or litmus tests.

I made some changes.  Maybe it's better now.