From: Paolo Valente <paolo.valente@linaro.org>
To: Jens Axboe <axboe@fb.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org,
Linux-Kernal <linux-kernel@vger.kernel.org>,
Omar Sandoval <osandov@fb.com>,
Linus Walleij <linus.walleij@linaro.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
Mark Brown <broonie@kernel.org>
Subject: Re: [PATCHSET v4] blk-mq-scheduling framework
Date: Thu, 26 Jan 2017 15:23:39 +0100 [thread overview]
Message-ID: <CAC36074-9BB6-4A35-94EA-73ACCFD6C86E@linaro.org> (raw)
In-Reply-To: <0e047692-5ff2-d404-a400-8484e060218b@fb.com>
> Il giorno 25 gen 2017, alle ore 17:13, Jens Axboe <axboe@fb.com> ha scritto:
>
> On 01/25/2017 01:46 AM, Paolo Valente wrote:
>>
>>> Il giorno 23 gen 2017, alle ore 18:42, Jens Axboe <axboe@fb.com> ha scritto:
>>>
>>> On 01/23/2017 10:04 AM, Paolo Valente wrote:
>>>>
>>>>> Il giorno 18 gen 2017, alle ore 17:21, Jens Axboe <axboe@fb.com> 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.
Yes, sorry. I'm already using blk_mq_sched_bypass_insert() to bypass
insertion in the insert hook, as done in mq-deadline, and I have no
get_request defined (see below).
The source of my confusion was that I assumed that flush requests had
not to leave any trace in the scheduler, since the scheduler does not
decide anything for them. Accordingly, I thought they did not trigger
any put or completion hook. In contrast, these requests get the
flag QUEUED set, in case the get_request hook is set, and then trigger
both a put_request and a completed_request. In this respect, in bfq-mq
I'm not using any of these three hooks (they are all NULL). I hope
I'm not doing something unexpected or incoherent.
UPDATE: bfq-mq now survives for minutes. I'm debugging two occasional
failures, which (un)fortunately become more and more occasional as I
go on with debugging and instrumenting the code.
Thanks,
Paolo
> 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
next prev parent reply other threads:[~2017-01-26 14:25 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-17 0:12 [PATCHSET v4] blk-mq-scheduling framework Jens Axboe
2016-12-17 0:12 ` [PATCH 1/8] block: move existing elevator ops to union Jens Axboe
2016-12-17 0:12 ` [PATCH 2/8] blk-mq: make mq_ops a const pointer Jens Axboe
2016-12-17 0:12 ` [PATCH 3/8] block: move rq_ioc() to blk.h Jens Axboe
2016-12-20 10:12 ` Paolo Valente
2016-12-20 15:46 ` Jens Axboe
2016-12-20 22:14 ` Jens Axboe
2016-12-17 0:12 ` [PATCH 4/8] blk-mq: un-export blk_mq_free_hctx_request() Jens Axboe
2016-12-17 0:12 ` [PATCH 5/8] blk-mq: export some helpers we need to the scheduling framework Jens Axboe
2016-12-17 0:12 ` [PATCH 6/8] blk-mq-sched: add framework for MQ capable IO schedulers Jens Axboe
2016-12-20 11:55 ` Paolo Valente
2016-12-20 15:45 ` Jens Axboe
2016-12-21 2:22 ` Jens Axboe
2016-12-22 15:20 ` Paolo Valente
2016-12-22 9:59 ` Paolo Valente
2016-12-22 11:13 ` Paolo Valente
2017-01-17 2:47 ` Jens Axboe
2017-01-17 10:13 ` Paolo Valente
2017-01-17 12:38 ` Jens Axboe
2016-12-23 10:12 ` Paolo Valente
2017-01-17 2:47 ` Jens Axboe
2017-01-17 9:17 ` Paolo Valente
2016-12-17 0:12 ` [PATCH 7/8] mq-deadline: add blk-mq adaptation of the deadline IO scheduler Jens Axboe
2016-12-20 9:34 ` Paolo Valente
2016-12-20 15:46 ` Jens Axboe
2016-12-21 11:59 ` Bart Van Assche
2016-12-21 14:22 ` Jens Axboe
2016-12-22 16:07 ` Paolo Valente
2017-01-17 2:47 ` Jens Axboe
2016-12-22 16:49 ` Paolo Valente
2017-01-17 2:47 ` Jens Axboe
2017-01-20 11:07 ` Paolo Valente
2017-01-20 14:26 ` Jens Axboe
2017-01-20 13:14 ` Paolo Valente
2017-01-20 13:18 ` Paolo Valente
2017-01-20 14:28 ` Jens Axboe
2017-01-20 14:28 ` Jens Axboe
2017-02-01 11:11 ` Paolo Valente
2017-02-02 5:19 ` Jens Axboe
2017-02-02 9:19 ` Paolo Valente
2017-02-02 15:30 ` Jens Axboe
2017-02-02 21:15 ` Paolo Valente
2017-02-02 21:32 ` Jens Axboe
2017-02-07 17:27 ` Paolo Valente
2017-02-01 11:56 ` Paolo Valente
2017-02-02 5:20 ` Jens Axboe
2017-02-16 10:46 ` Paolo Valente
2017-02-16 15:35 ` Jens Axboe
2016-12-17 0:12 ` [PATCH 8/8] blk-mq-sched: allow setting of default " Jens Axboe
2016-12-19 11:32 ` [PATCHSET v4] blk-mq-scheduling framework Paolo Valente
2016-12-19 15:20 ` Jens Axboe
2016-12-19 15:33 ` Jens Axboe
2016-12-19 18:21 ` Paolo Valente
2016-12-19 21:05 ` Jens Axboe
2016-12-22 15:28 ` Paolo Valente
2017-01-17 2:47 ` Jens Axboe
2017-01-17 10:49 ` Paolo Valente
2017-01-18 16:14 ` Paolo Valente
2017-01-18 16:21 ` Jens Axboe
2017-01-23 17:04 ` Paolo Valente
2017-01-23 17:42 ` Jens Axboe
2017-01-25 8:46 ` Paolo Valente
2017-01-25 16:13 ` Jens Axboe
2017-01-26 14:23 ` Paolo Valente [this message]
2016-12-22 16:23 ` Bart Van Assche
2016-12-22 16:52 ` Omar Sandoval
2016-12-22 16:57 ` Bart Van Assche
2016-12-22 17:12 ` Omar Sandoval
2016-12-22 17:39 ` Bart Van Assche
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