Messages in this thread | | | Date | Thu, 19 Mar 2009 09:06:41 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 06/13] async_tx: add support for asynchronous GF multiplication |
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Dan Williams wrote: > + * @scfs: array of source coefficients used in GF-multiplication
Array of source coefficients? Are you doing a vector-vector multiplication here?
Given this code:
> for (d = 0; d < len; d++) { > + wq = wp = ptrs[0][d]; > + for (z = 1; z < src_cnt; z++) { > + wd = ptrs[z][d]; > + wp ^= wd; > + wq ^= raid6_gfmul[scfs[z]][wd]; > + }
... it kinds of looks like that.
This is really quite expensive! The whole point of the restore code that exists is that we never do a two-dimensional lookup, instead caching a pointer to the multiplication table that we intend to use, because the RAID-6 code only ever contains scalar-vector multiplications.
I really don't get this, and I think it's broken.
-hpa
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