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>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c712460..456c3c2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -574,8 +574,7 @@
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 @@
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 @@
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);