Re: [PATCHSET v4] blk-mq-scheduling framework

From: Paolo Valente
Date: Wed Jan 25 2017 - 03:46:53 EST

> Il giorno 23 gen 2017, alle ore 18:42, Jens Axboe <axboe@xxxxxx> ha scritto:
> On 01/23/2017 10:04 AM, Paolo Valente wrote:
>>> Il giorno 18 gen 2017, alle ore 17:21, Jens Axboe <axboe@xxxxxx> ha scritto:
>>> On 01/18/2017 08:14 AM, Paolo Valente wrote:
>>>> according to the function blk_mq_sched_put_request, the
>>>> mq.completed_request hook seems to always be invoked (if set) for a
>>>> request for which the mq.put_rq_priv is invoked (if set).
>>> Correct, any request that came out of blk_mq_sched_get_request()
>>> will always have completed called on it, regardless of whether it
>>> had IO started on it or not.
>> It seems that some request, after being dispatched, happens to have no
>> mq.put_rq_priv invoked on it now or then. Is it expected? If it is,
>> could you point me to the path through which the end of the life of
>> such a request is handled?
> I'm guessing that's a flush request. I added RQF_QUEUED to check for
> that, if RQF_QUEUED is set, you know it has come from your get_request
> handler.

Exactly, the completion-without-put_rq_priv pattern seems to occur
only for requests coming from the flusher, precisely because they have
the flag RQF_ELVPRIV unset. Just to understand: why is this flag
unset for these requests, if they do have private elevator (bfq)
data attached? What am I misunderstanding?

Just to be certain: this should be the only case where the
completed_request hook is invoked while the put_rq_priv is not, right?


> I'm assuming that is it, let me know.
> --
> Jens Axboe