From: Jens Axboe <axboe@kernel.dk>
To: Omar Sandoval <osandov@osandov.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
Omar Sandoval <osandov@fb.com>
Subject: Re: [PATCH] blk-mq: fix sbitmap ws_active for shared tags
Date: Mon, 25 Mar 2019 12:58:47 -0600 [thread overview]
Message-ID: <5ed3aa61-e12d-2dc4-2a8d-e9cc02788371@kernel.dk> (raw)
In-Reply-To: <20190325185635.GF5826@vader>
On 3/25/19 12:56 PM, Omar Sandoval wrote:
> On Mon, Mar 25, 2019 at 10:22:50AM -0600, Jens Axboe wrote:
>> We now wrap sbitmap waitqueues in an active counter, so we can avoid
>> iterating wakeups unless we have waiters there. This works as long as
>> everyone that's manipulating the waitqueues use the proper helpers. For
>> the tag wait case for shared tags, however, we add ourselves to the
>> waitqueue without incrementing/decrementing the ->ws_active count. This
>> means that wakeups can take a long time to happen.
>>
>> Fix this by manually doing the inc/dec as needed for the wait queue
>> handling.
>>
>> Fixes: 5d2ee7122c73 ("sbitmap: optimize wakeup check")
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
> Can this use the helpers we added in 9f6b7ef6c3eb ("sbitmap: add helpers
> for add/del wait queue handling")?
I don't think so without adding more, which seems kind of silly for this
very specialized use case of openly manipulating the wait queues. The
blk-mq setup there is very special cased.
--
Jens Axboe
next prev parent reply other threads:[~2019-03-25 18:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-25 16:22 [PATCH] blk-mq: fix sbitmap ws_active for shared tags Jens Axboe
2019-03-25 16:39 ` Bart Van Assche
2019-03-25 16:42 ` Jens Axboe
2019-03-25 18:56 ` Omar Sandoval
2019-03-25 18:58 ` Jens Axboe [this message]
2019-03-25 19:04 ` Omar Sandoval
2019-03-25 19:05 ` Jens Axboe
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