Re: [RFC PATCH] sbitmap: fix batching wakeup

[Jens Axboe <axboe@kernel.dk>]

On 7/21/23 3:57?AM, Ming Lei wrote:
> From: David Jeffery <djeffery@redhat.com>
> 
> Current code supposes that it is enough to provide forward progress by just
> waking up one wait queue after one completion batch is done.
> 
> Unfortunately this way isn't enough, cause waiter can be added to
> wait queue just after it is woken up.
> 
> Follows one example(64 depth, wake_batch is 8)
> 
> 1) all 64 tags are active
> 
> 2) in each wait queue, there is only one single waiter
> 
> 3) each time one completion batch(8 completions) wakes up just one waiter in each wait
> queue, then immediately one new sleeper is added to this wait queue
> 
> 4) after 64 completions, 8 waiters are wakeup, and there are still 8 waiters in each
> wait queue
> 
> 5) after another 8 active tags are completed, only one waiter can be wakeup, and the other 7
> can't be waken up anymore.
> 
> Turns out it isn't easy to fix this problem, so simply wakeup enough waiters for
> single batch.

Change looks good, but commit message needs:

1) Signed-off-by from author
2) To be wrapped at ~72 chars, it's got lines that are way too long.

I can edit the commit message, but David does need to reply with his SOB
before it can get applied.

-- 
Jens Axboe