Hi Andreas, The per_chunk_alignment addresses a backward compatible change in the way they are calculated. The problem was that the initial calculation lead to oversized chunks. The long explanation is at https://github.com/ceph/ceph/commit/c7daaaf5e63d0bd1d444385e62611fe276f6ce29 Please let me know if you see something wrong :-) Cheers On 18/09/2014 14:34, Andreas Joachim Peters wrote: > Hi Janne/Loic, > there is more confusion atleast on my side ... > > I had now a look at the jerasure plug-in and I am now slightly confused why you have two ways to return in get_alignment ... one is as I assume and another one is "per_chunk_alignment" ... what should the function return Loic? > > Cheers Andreas. > ________________________________________ > From: ceph-devel-owner@xxxxxxxxxxxxxxx [ceph-devel-owner@xxxxxxxxxxxxxxx] on behalf of Andreas Joachim Peters [Andreas.Joachim.Peters@xxxxxxx] > Sent: 18 September 2014 14:18 > To: Janne Grunau; ceph-devel@xxxxxxxxxxxxxxx > Subject: RE: v2 aligned buffer changes for erasure codes > > Hi Janne, > => (src/erasure-code/isa/README claims it needs 16*k byte aligned buffers > > I should update the README since it is misleading ... it should say 8*k or 16*k byte aligned chunk size depending on the compiler/platform used, it is not the alignment of the allocated buffer addresses.The get_alignment in the plug-in function is used to compute the chunk size for the encoding (as I said not the start address alignment). > > If you pass k buffers for decoding each buffer should be aligned at least to 16 or as you pointed out better 32 bytes. > > For encoding there is normally a single buffer split 'virtually' into k pieces. To make all pieces starting at an aligned address one needs to align the chunk size to e.g. 16*k. For the best possible performance on all platforms we should change the get_alignment function in the ISA plug-in to return 32*k if there are no other objections ?!?! > > Cheers Andreas. > ________________________________________ > From: ceph-devel-owner@xxxxxxxxxxxxxxx [ceph-devel-owner@xxxxxxxxxxxxxxx] on behalf of Janne Grunau [j@xxxxxxxxxx] > Sent: 18 September 2014 12:33 > To: ceph-devel@xxxxxxxxxxxxxxx > Subject: v2 aligned buffer changes for erasure codes > > Hi, > > following a is an updated patchset. It passes now make check in src > > It has following changes: > * use 32-byte alignment since the isa plugin use AVX2 > (src/erasure-code/isa/README claims it needs 16*k byte aligned buffers > but I can't see a reason why it would need more than 32-bytes > * ErasureCode::encode_prepare() handles more than one chunk with padding > > cheers > > Janne > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Loïc Dachary, Artisan Logiciel Libre
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