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Subject[PATCH 028 of 29] md: md: handle operation chaining in raid5_run_ops

From: Dan Williams <dan.j.williams@intel.com>

Neil said:
> At the end of ops_run_compute5 you have:
> /* ack now if postxor is not set to be run */
> if (tx && !test_bit(STRIPE_OP_POSTXOR, &s->ops_run))
> async_tx_ack(tx);
>
> It looks odd having that test there. Would it fit in raid5_run_ops
> better?

The intended global interpretation is that raid5_run_ops can build a chain
of xor and memcpy operations. When MD registers the compute-xor it tells
async_tx to keep the operation handle around so that another item in the
dependency chain can be submitted. If we are just computing a block to
satisfy a read then we can terminate the chain immediately. raid5_run_ops
gives a better context for this test since it cares about the entire chain.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/raid5.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c
--- .prev/drivers/md/raid5.c 2008-06-27 16:42:56.000000000 +1000
+++ ./drivers/md/raid5.c 2008-06-27 16:42:56.000000000 +1000
@@ -574,8 +574,7 @@ static void ops_complete_compute5(void *
release_stripe(sh);
}

-static struct dma_async_tx_descriptor *
-ops_run_compute5(struct stripe_head *sh, unsigned long ops_request)
+static struct dma_async_tx_descriptor *ops_run_compute5(struct stripe_head *sh)
{
/* kernel stack size limits the total number of disks */
int disks = sh->disks;
@@ -605,10 +604,6 @@ ops_run_compute5(struct stripe_head *sh,
ASYNC_TX_XOR_ZERO_DST, NULL,
ops_complete_compute5, sh);

- /* ack now if postxor is not set to be run */
- if (tx && !test_bit(STRIPE_OP_POSTXOR, &ops_request))
- async_tx_ack(tx);
-
return tx;
}

@@ -813,8 +808,12 @@ static void raid5_run_ops(struct stripe_
overlap_clear++;
}

- if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request))
- tx = ops_run_compute5(sh, ops_request);
+ if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
+ tx = ops_run_compute5(sh);
+ /* terminate the chain if postxor is not set to be run */
+ if (tx && !test_bit(STRIPE_OP_POSTXOR, &ops_request))
+ async_tx_ack(tx);
+ }

if (test_bit(STRIPE_OP_PREXOR, &ops_request))
tx = ops_run_prexor(sh, tx);

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