Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

Jens Axboe
2014-06-04T16:25:28Z

On 06/04/2014 09:47 AM, Jens Axboe wrote:
> On 06/04/2014 09:39 AM, Jens Axboe wrote:
>> On 06/04/2014 09:31 AM, Christoph Hellwig wrote:
>>> On Wed, Jun 04, 2014 at 09:02:19AM -0600, Jens Axboe wrote:
>>>>> scsi_mq_find_tag only gets the scsi host, which may have multiple
>>>>> queues. When called from scsi_find_tag we actually have a scsi device,
>>>>> so that's not an issue, but when called from scsi_host_find_tag the
>>>>> driver only provides the host.
>>>>
>>>> Only solution I see right now is to have the flush_rq in the shared
>>>> tags, but that would potentially be a regression for multiple
>>>> devices and heavy flush uses cases. I'll see if I can come up with
>>>> something better, or maybe Shaohua has an idea.
>>>
>>> What about something like the following (untest, uncompiled, maybe
>>> pseudo-code):
>>>
>>> struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
>>> {
>>> struct request *rq = tags->rqs[tag];
>>>
>>> if ((rq->cmd_flags & REQ_FLUSH_SEQ) && rq->q->flush_rq->tag == tag)
>>> return rq->q->flush_rq;
>>> return rq;
>>
>> Ah yes, that'll work, the queue is always assigned. I'll make that change.
>
> Something like this in complete form. Compile tested only, I'll test it
> on dev box. Probably doesn't matter too much, but I prefer to
> potentially have the faster path (non-flush) just fall inline.

Works for me, committed.

--
Jens Axboe