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From: Kanchan Joshi <[email protected]>
To: Christoph Hellwig <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	Anuj Gupta <[email protected]>
Subject: Re: [PATCH for-next v7 4/5] block: add helper to map bvec iterator for passthrough
Date: Tue, 27 Sep 2022 22:17:26 +0530	[thread overview]
Message-ID: <20220927164726.GA23874@test-zns> (raw)
In-Reply-To: <[email protected]>

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On Mon, Sep 26, 2022 at 04:50:40PM +0200, Christoph Hellwig wrote:
>On Sat, Sep 24, 2022 at 12:13:49AM +0530, Kanchan Joshi wrote:
>> And efficency is the concern as we are moving to more heavyweight
>> helper that 'handles' weird conditions rather than just 'bails out'.
>> These alignment checks end up adding a loop that traverses
>> the entire ITER_BVEC.
>> Also blk_rq_map_user_iov uses bio_iter_advance which also seems
>> cycle-consuming given below code-comment in io_import_fixed():
>
>No one says you should use the existing loop in blk_rq_map_user_iov.
>Just make it call your new helper early on when a ITER_BVEC iter is
>passed in.

Indeed. I will send the v10 with that approach.

>> Do you see good way to trigger this virt-alignment condition? I have
>> not seen this hitting (the SG gap checks) when running with fixebufs.
>
>You'd need to make sure the iovec passed to the fixed buffer
>registration is chunked up smaller than the nvme page size.
>
>E.g. if you pass lots of non-contiguous 512 byte sized iovecs to the
>buffer registration.
>
>>> We just need to implement the equivalent functionality for bvecs.  It
>>> isn't really hard, it just wasn't required so far.
>>
>> Can the virt-boundary alignment gap exist for ITER_BVEC iter in first
>> place?
>
>Yes.  bvecs are just a way to represent data.  If the individual
>segments don't fit the virt boundary you still need to deal with it.

Thanks for clearing this.

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  reply	other threads:[~2022-09-27 16:58 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20220909103131epcas5p23d146916eccedf30d498e0ea23e54052@epcas5p2.samsung.com>
2022-09-09 10:21 ` [PATCH for-next v7 0/5] fixed-buffer for uring-cmd/passthru Kanchan Joshi
     [not found]   ` <CGME20220909103136epcas5p38ea3a933e90d9f9d7451848dc3a60829@epcas5p3.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 1/5] io_uring: add io_uring_cmd_import_fixed Kanchan Joshi
     [not found]   ` <CGME20220909103140epcas5p36689726422eb68e6fdc1d39019a4a8ba@epcas5p3.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 2/5] io_uring: introduce fixed buffer support for io_uring_cmd Kanchan Joshi
     [not found]   ` <CGME20220909103143epcas5p2eda60190cd23b79fb8f48596af3e1524@epcas5p2.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 3/5] nvme: refactor nvme_alloc_user_request Kanchan Joshi
2022-09-20 12:02       ` Christoph Hellwig
2022-09-22 15:46         ` Kanchan Joshi
2022-09-23  9:25         ` Kanchan Joshi
     [not found]   ` <CGME20220909103147epcas5p2a83ec151333bcb1d2abb8c7536789bfd@epcas5p2.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 4/5] block: add helper to map bvec iterator for passthrough Kanchan Joshi
2022-09-20 12:08       ` Christoph Hellwig
2022-09-22 15:23         ` Kanchan Joshi
2022-09-23 15:29           ` Christoph Hellwig
2022-09-23 18:43             ` Kanchan Joshi
2022-09-25 17:46               ` Kanchan Joshi
2022-09-26 14:50               ` Christoph Hellwig
2022-09-27 16:47                 ` Kanchan Joshi [this message]
     [not found]   ` <CGME20220909103151epcas5p1e25127c3053ba21e8f8418a701878973@epcas5p1.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 5/5] nvme: wire up fixed buffer support for nvme passthrough Kanchan Joshi

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