Re: [PATCH 06/13] async_tx: add support for asynchronous GF multiplication

On Fri, Mar 20, 2009 at 7:30 PM, H. Peter Anvin [off-list ref] wrote:

Ilya Yanok wrote:

quoted

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...

quoted

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;
 }
-EXPORT_SYMBOL_GPL(async_pq);

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.

Thanks,
Dan