Messages in this thread | | | From | Waiman Long <> | Subject | Re: [PATCH] docs: lockdep-design: correct the notation for writer | Date | Mon, 24 May 2021 09:42:20 -0400 |
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On 5/24/21 6:32 AM, Boqun Feng wrote: > On Mon, May 24, 2021 at 12:24:00PM +0800, Xiongwei Song wrote: >> On Fri, May 21, 2021 at 11:17 PM Waiman Long <llong@redhat.com> wrote: >>> On 5/21/21 2:29 AM, Xiongwei Song wrote: >>>> From: Xiongwei Song <sxwjean@gmail.com> >>>> >>>> The block condition matrix is using 'E' as the writer noation here, so it >>>> would be better to use 'E' as the reminder rather than 'W'. >>>> >>>> Signed-off-by: Xiongwei Song <sxwjean@gmail.com> >>>> --- >>>> Documentation/locking/lockdep-design.rst | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/Documentation/locking/lockdep-design.rst b/Documentation/locking/lockdep-design.rst >>>> index 9f3cfca..c3b923a 100644 >>>> --- a/Documentation/locking/lockdep-design.rst >>>> +++ b/Documentation/locking/lockdep-design.rst >>>> @@ -462,7 +462,7 @@ Block condition matrix, Y means the row blocks the column, and N means otherwise >>>> | R | Y | Y | N | >>>> +---+---+---+---+ >>>> >>>> - (W: writers, r: non-recursive readers, R: recursive readers) >>>> + (E: writers, r: non-recursive readers, R: recursive readers) >>>> >>>> >>>> acquired recursively. Unlike non-recursive read locks, recursive read locks >>> I would say it should be the other way around. Both W and E refer to the >>> same type of lockers. W emphasizes writer aspect of it and E for >>> exclusive. I think we should change the block condition matrix to use W >>> instead of E. >> The doc uses 'E' to describe dependency egdes too. Should we change them >> to 'W'? Personally, both 'W' and 'E' are fine. >> > I also think Waiman's suggestion is solid, there are two ways to > classify locks: > > 1. W (Writers), R (Recursive Readers), r (Non-recursive Readers) > > 2. E (Exclusive locks), S (Shared locks), R (Recursive Readers), > N (Non-recursive locks) > > And the relations between them are as follow: > > E = W > R = R > N = W \/ r > S = R \/ r > > , where "\/" is the set union. > > The story is that I used the way #1 at first, and later on realized way > #2 is better for BFS implementation, also for reasoning, so here came > this leftover.. > My suggestion was based on the fact that it is harder to associate E with writer. So from a readability perspective, it is better to change the block condition matrix to use 'W' to make it more readable.
Cheers, Longman
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