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SubjectRe: [PATCH] docs: lockdep-design: correct the notation for writer
Date
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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