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>, <osandov@fb.com>
Subject: Re: [PATCH 6/8] blk-mq-sched: add framework for MQ capable IO schedulers
Date: Mon, 16 Jan 2017 18:47:22 -0800 [thread overview]
Message-ID: <c36a39ee-d0af-017e-590a-bf5d5ede065c@fb.com> (raw)
In-Reply-To: <9936D33B-AE98-46DF-B1DA-D54142A338FD@linaro.org>
On 12/22/2016 02:59 AM, Paolo Valente wrote:
>
>> Il giorno 17 dic 2016, alle ore 01:12, Jens Axboe <axboe@fb.com> ha scritto:
>>
>> This adds a set of hooks that intercepts the blk-mq path of
>> allocating/inserting/issuing/completing requests, allowing
>> us to develop a scheduler within that framework.
>>
>> We reuse the existing elevator scheduler API on the registration
>> side, but augment that with the scheduler flagging support for
>> the blk-mq interfce, and with a separate set of ops hooks for MQ
>> devices.
>>
>> Schedulers can opt in to using shadow requests. Shadow requests
>> are internal requests that the scheduler uses for for the allocate
>> and insert part, which are then mapped to a real driver request
>> at dispatch time. This is needed to separate the device queue depth
>> from the pool of requests that the scheduler has to work with.
>>
>> Signed-off-by: Jens Axboe <axboe@fb.com>
>>
> ...
>
>> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
>> new file mode 100644
>> index 000000000000..b7e1839d4785
>> --- /dev/null
>> +++ b/block/blk-mq-sched.c
>
>> ...
>> +static inline bool
>> +blk_mq_sched_allow_merge(struct request_queue *q, struct request *rq,
>> + struct bio *bio)
>> +{
>> + struct elevator_queue *e = q->elevator;
>> +
>> + if (e && e->type->ops.mq.allow_merge)
>> + return e->type->ops.mq.allow_merge(q, rq, bio);
>> +
>> + return true;
>> +}
>> +
>
> Something does not seem to add up here:
> e->type->ops.mq.allow_merge may be called only in
> blk_mq_sched_allow_merge, which, in its turn, may be called only in
> blk_mq_attempt_merge, which, finally, may be called only in
> blk_mq_merge_queue_io. Yet the latter may be called only if there is
> no elevator (line 1399 and 1507 in blk-mq.c).
>
> Therefore, e->type->ops.mq.allow_merge can never be called, both if
> there is and if there is not an elevator. Be patient if I'm missing
> something huge, but I thought it was worth reporting this.
I went through the current branch, and it seems mostly fine. There was
a double call to allow_merge() that I killed in the plug path, and one
set missing in blk_mq_sched_try_merge(). The rest looks OK.
--
Jens Axboe
next prev parent reply other threads:[~2017-01-17 2:48 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 [this message]
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
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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