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From: Jens Axboe <axboe@fb.com>
To: Paolo Valente <paolo.valente@linaro.org>
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: Wed, 25 Jan 2017 09:13:35 -0700	[thread overview]
Message-ID: <0e047692-5ff2-d404-a400-8484e060218b@fb.com> (raw)
In-Reply-To: <15FC1715-D77C-4E31-811B-60898C0C6DAA@linaro.org>

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.
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

  reply	other threads:[~2017-01-25 16:13 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 [this message]
2017-01-26 14:23                           ` Paolo Valente
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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