On 01/25/2017 01:46 AM, Paolo Valente wrote: > >> 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? They must NOT have scheduler data attached. In your get_request function, you must bypass if blk_mq_sched_bypass_insert() returns true. See how mq-deadline does that. This is important, or you will get hangs with flushes as well, since the IO scheduler private data and the flush data is unionized in the request. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
