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    SubjectRe: [PATCH 06/13] async_tx: add support for asynchronous GF multiplication
    On Fri, Mar 20, 2009 at 7:30 PM, H. Peter Anvin <> wrote:
    > Ilya Yanok wrote:
    >> async_gen_syndrome() takes element of GF^n(256) and returns result of
    >> scalar multiplication of it with constant ({01}, {02}, {02}^2, ...,
    >> {02}^n) vector.
    > For any n (which would mean any GF field)?  In that case, that is
    > generic scalar-vector multiplication...
    >> async_pq() takes two vectors from GF^n(256) and returns their scalar
    >> multiplication.
    >> We need async_pq() function if we want to offload D_x = A * (P + P_{xy})
    >> + B * (Q + Q_{xy}) part of DD recovery and D_x = (Q + Q_x) * g^{-x} part
    >> of DP recovery.
    > No, you don't.  A and B (and g^{-x}) are scalars, meaning they're the
    > same for every element.  This is simpler to do.

    Understood. However this routine also needs to cover the non-generic
    and non-constant case where we have a separate coefficient per
    element. I suppose it could scan the coefficient list to see if it
    can bypass the 2-dimensional lookup multiply. At the very least we
    need something like the following, because async_pq is really only a
    helper routine for async_r6recov.c which knows how to avoid the
    synchronous path.

    diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
    index da47a29..c1087a2 100644
    --- a/crypto/async_tx/async_pq.c
    +++ b/crypto/async_tx/async_pq.c
    @@ -236,6 +236,7 @@ async_pq(struct page **blocks, unsigned int
    offset, int src_cnt,
    flags, depend_tx, cb_fn, cb_param);
    } else {
    /* run pq synchronously */
    + WARN_ONCE(1, "INFO: async_pq entered synchronous path\n");
    if (!blocks[src_cnt+1]) { /* only p requested, just xor */
    flags |= ASYNC_TX_XOR_ZERO_DST;
    return async_xor(blocks[src_cnt], blocks, offset,
    @@ -252,7 +253,6 @@ async_pq(struct page **blocks, unsigned int
    offset, int src_cnt,

    return tx;

    Looking closer, the only other caller, async_pq_zero_sum, can be
    deleted because it has no users. So async_pq can become a static
    routine in async_r6recov.

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      Last update: 2009-03-21 16:23    [W:0.025 / U:18.096 seconds]
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