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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>
This commit is contained in:
Dan Williams 2008-06-28 08:32:09 +10:00 committed by Neil Brown
parent d8ee0728b5
commit 7b3a871ed9
1 changed files with 7 additions and 8 deletions
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15
drivers/md/raid5.c
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@ -574,8 +574,7 @@ static void ops_complete_compute5(void *stripe_head_ref)
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, unsigned long ops_request)
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_head *sh, unsigned long ops_request)
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);