Buffer alignment

Buffer alignment

[Loic Dachary]

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Hi Andreas,

In Ceph, buffers can be aligned if required using buffer::create_page_aligned

https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L519
https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L230

and although the Jerasure plugin has alignment requirements

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L79

it did not occur to me that aligning the buffers used to stored the encoded 

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L87

result would be needed. For decoding the caller is responsible for allocating the buffers. For encoding it also is, except for the padding. 

Do you think the API should recommend something regarding alignment ? 

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodeInterface.h#L20

Cheers

-- 
Loïc Dachary, Artisan Logiciel Libre


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RE: Buffer alignment

[Andreas Joachim Peters]

Hi Loic, 
if you pull the BPC extension this requires 128-bit aligned memory adresses, maybe to prepare for future extensions they should be even 512-bit aligned. I can add an assertion if I see unaligned addresses.

Cheers Andreas.

________________________________________
From: Loic Dachary [loic@dachary.org]
Sent: 10 December 2013 09:32
To: Andreas Joachim Peters
Cc: Ceph Development
Subject: Buffer alignment

Hi Andreas,

In Ceph, buffers can be aligned if required using buffer::create_page_aligned

https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L519
https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L230

and although the Jerasure plugin has alignment requirements

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L79

it did not occur to me that aligning the buffers used to stored the encoded

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L87

result would be needed. For decoding the caller is responsible for allocating the buffers. For encoding it also is, except for the padding.

Do you think the API should recommend something regarding alignment ?

https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodeInterface.h#L20

Cheers

--
Loïc Dachary, Artisan Logiciel Libre

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Re: Buffer alignment

[Loic Dachary]

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On 11/12/2013 10:50, Andreas Joachim Peters wrote:
> Hi Loic, 
> if you pull the BPC extension this requires 128-bit aligned memory adresses, maybe to prepare for future extensions they should be even 512-bit aligned. I can add an assertion if I see unaligned addresses.
> 

Could you please remind me which branch of your repository I should look at ?

Cheers

> Cheers Andreas.
> 
> ________________________________________
> From: Loic Dachary [loic@dachary.org]
> Sent: 10 December 2013 09:32
> To: Andreas Joachim Peters
> Cc: Ceph Development
> Subject: Buffer alignment
> 
> Hi Andreas,
> 
> In Ceph, buffers can be aligned if required using buffer::create_page_aligned
> 
> https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L519
> https://github.com/ceph/ceph/blob/master/src/common/buffer.cc#L230
> 
> and although the Jerasure plugin has alignment requirements
> 
> https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L79
> 
> it did not occur to me that aligning the buffers used to stored the encoded
> 
> https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodePluginJerasure/ErasureCodeJerasure.cc#L87
> 
> result would be needed. For decoding the caller is responsible for allocating the buffers. For encoding it also is, except for the padding.
> 
> Do you think the API should recommend something regarding alignment ?
> 
> https://github.com/ceph/ceph/blob/master/src/osd/ErasureCodeInterface.h#L20
> 
> Cheers
> 
> --
> Loïc Dachary, Artisan Logiciel Libre
> 
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> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

-- 
Loïc Dachary, Artisan Logiciel Libre


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