On 3/25/19 1:04 PM, Omar Sandoval wrote:
> On Mon, Mar 25, 2019 at 12:58:47PM -0600, Jens Axboe wrote:
>> 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@xxxxxxxxx>
>>>
>>> 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.
>
> Yup, I see. Assuming it fixes the issue,
>
> Reviewed-by: Omar Sandoval <osandov@xxxxxx>
Thanks - it does fix the issue, the original reporter has since tested and
confirmed that his abysmally slow raid5 now works at full speed again.
--
Jens Axboe
