On Thursday, January 15, 2009 Dan Williams wrote:
> On Mon, Jan 12, 2009 at 5:43 PM, Yuri Tikhonov <yur@xxxxxxxxxxx> wrote:
>> + /* (2) Calculate Q+Qxy */
>> + lptrs[0] = ptrs[failb];
>> + lptrs[1] = ptrs[disks-1];
>> + lptrs[2] = NULL;
>> + tx = async_pq(lptrs, NULL, 0, 1, bytes, ASYNC_TX_DEP_ACK,
>> + tx, NULL, NULL);
>> +
>> + /* (3) Calculate P+Pxy */
>> + lptrs[0] = ptrs[faila];
>> + lptrs[1] = ptrs[disks-2];
>> + lptrs[2] = NULL;
>> + tx = async_pq(lptrs, NULL, 0, 1, bytes, ASYNC_TX_DEP_ACK,
>> + tx, NULL, NULL);
>> +
> These two calls convinced me that ASYNC_TX_PQ_ZERO_{P,Q} need to go.
> A 1-source async_pq operation does not make sense.
Another source is hidden under not-set ASYNC_TX_PQ_ZERO_{P,Q} :)
Though, I agree, this looks rather misleading.
> These should be:
> /* (2) Calculate Q+Qxy */
> lptrs[0] = ptrs[disks-1];
> lptrs[1] = ptrs[failb];
> tx = async_xor(lptrs[0], lptrs, 0, 2, bytes,
> ASYNC_TX_XOR_DROP_DST|ASYNC_TX_DEP_ACK, tx, NULL, NULL);
> /* (3) Calculate P+Pxy */
> lptrs[0] = ptrs[disks-2];
> lptrs[1] = ptrs[faila];
> tx = async_xor(lptrs[0], lptrs, 0, 2, bytes,
> ASYNC_TX_XOR_DROP_DST|ASYNC_TX_DEP_ACK, tx, NULL, NULL);
The reason why I preferred to use async_pq() instead of async_xor()
here is to maximize the chance that the whole D+D recovery operation
will be handled in one ADMA device, i.e. without channels switch and
the latency introduced because of that.
So, if we'll decide to stay with ASYNC_TX_PQ_ZERO_{P,Q}, then this
should be probably kept unchanged, but if we'll get rid of
ASYNC_TX_PQ_ZERO_{P,Q}, then, obviously, we'll have to use
async_xor()s here as you suggest.
Regards, Yuri
--
Yuri Tikhonov, Senior Software Engineer
Emcraft Systems, www.emcraft.com
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