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From: Bart Van Assche <>
To: Niklas Cassel <>
Cc: Jens Axboe <>,
	Damien Le Moal <>,
	Paolo Valente <>,
	Ming Lei <>,
	"" <>,
	"" <>
Subject: Re: [PATCH 2/2] Revert "mq-deadline: Fix request accounting"
Date: Tue, 7 Sep 2021 10:12:49 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <YTeTQGrw41k08hgf@x1-carbon>

On 9/7/21 9:28 AM, Niklas Cassel wrote:
> On Tue, Sep 07, 2021 at 08:15:03AM -0700, Bart Van Assche wrote:
>> On 9/7/21 7:21 AM, Niklas Cassel wrote:
>>> blk-mq will no longer call the I/O scheduler .finish_request() callback
>>> for requests that were never inserted to the I/O scheduler.
>> I do not agree. Even with patch 1/2 from this series applied, finish_request()
>> will still be called for requests inserted by blk_insert_cloned_request()
>> although these requests are never inserted to the I/O scheduler.
> Looking at blk_mq_free_request(),
> e->type->ops.finish_request() will only be called if RQF_ELVPRIV
> is set.
> blk_insert_cloned_request() doesn't seem to allocate a request
> itself, but instead takes an already cloned request.
> So I guess it depends on how the supplied request was cloned.
> I would assume if the original request doesn't have RQF_ELVPRIV set,
> then neither will the cloned request?
> I tried to look at blk_rq_prep_clone(), which seems to be a common
> cloning function, but I don't see req->rq_flags being copied
> (except for RQF_SPECIAL_PAYLOAD).
> Anyway, I don't see how .finish_request() will be called in relation
> to blk_insert_cloned_request(). Could you please help me out and
> give me an example of a call chain where this can happen?

Hi Niklas,

This is a bit outside my area of expertise. Anyway: map_request() calls
.clone_and_map_rq(). At least multipath_clone_and_map() calls
blk_get_request(). I think this shows that blk_insert_cloned_request()
may insert an entirely new request. Is my understanding correct that
blk_mq_rq_ctx_init() will set RQF_ELVPRIV for the cloned request if a
scheduler is associated with the request queue associated with the
cloned request?


  reply	other threads:[~2021-09-07 17:12 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-07 14:21 [PATCH 0/2] don't call io scheduler callbacks for passthrough requests Niklas Cassel
2021-09-07 14:21 ` [PATCH 1/2] blk-mq: don't call callbacks for requests that bypassed the scheduler Niklas Cassel
2021-09-07 14:29   ` Ming Lei
2021-09-07 14:21 ` [PATCH 2/2] Revert "mq-deadline: Fix request accounting" Niklas Cassel
2021-09-07 14:54   ` Bart Van Assche
2021-09-07 16:07     ` Niklas Cassel
2021-09-07 16:49       ` Bart Van Assche
2021-09-07 15:15   ` Bart Van Assche
2021-09-07 16:28     ` Niklas Cassel
2021-09-07 17:12       ` Bart Van Assche [this message]
2021-09-08 11:57         ` Niklas Cassel

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