From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bart Van Assche <bvanassche-HInyCGIudOg@public.gmane.org>
Subject: Re: linux rdma 3.14 merge plans
Date: Wed, 29 Jan 2014 18:56:02 +0100
Message-ID: <52E940B2.3070901@acm.org>
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To: Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>, Or Gerlitz <or.gerlitz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Roland Dreier <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Hefty Sean <sean.hefty-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: linux-rdma <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Mike Christie <michaelc-hcNo3dDEHLuVc3sceRu5cw@public.gmane.org>, Oren Duer <oren-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
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On 01/29/14 16:06, Sagi Grimberg wrote:
> On 1/29/2014 4:13 PM, Bart Van Assche wrote:
>> Would one of the options below perhaps be an
>> appropriate solution ?
>> - Add a flag in struct request_queue that tells the block layer to use a
>>    bounce buffer (data copying) for I/O requests with a discontiguous
>>    data buffer. The block layer already supports copying data buffers for
>>    which e.g. DMA alignment requirements are not met. Rework patch
>>    "IB/iser: Introduce fast memory registration model" (commit
>>    5587856c9659ac2d6ab201141aa8a5c2ff3be4cd) such that it takes advantage
>>    of that new flag. See also blk_rq_map_user_iov() for an example of
>>    how the block layer decides when copying a data buffer is necessary.
> 
> Didn't understand why should it matter where the copy is done (iser/block)?

In the Linux kernel community it is considered important to avoid code
duplication. Hence the proposal to keep code that copies data buffers in
the block layer core and to avoid that such functionality has to be
reimplemented in every block driver or SCSI LLD.

Bart.

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