On 11/9/18 9:53 AM, jianchao.wang wrote:
> Hi Jens
>
> On 11/9/18 12:06 AM, Jens Axboe wrote:
>> DM currently uses atomic inc/dec to maintain a busy count of
>> IO on a given device. For the dm-mq path, we can replace this
>> with helper that just checks the state of the tags on the device.
>>
>> First patch is a prep patch that allows the iteration helpers
>> to return true/false, like we support internally in sbitmap.
>> For a busy check we don't care about how many requests are
>> busy, just if some are or not. Hence we can stop iterating
>> tags as soon as we find one that is allocated.
>
> If we don't care about how many requests are busy, why not check
> sb->map[idex].word directly ? It could be more efficient.
>
Oh, we need to check rq->q for the tag shared case.
> Thanks
> Jianchao
>
