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@xxxxxxxxxx> wrote:
On 5/21/21 2:29 AM, Xiongwei Song wrote:
From: Xiongwei Song <sxwjean@xxxxxxxxx>
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@xxxxxxxxx>
---
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
