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md: kill STRIPE_OP_MOD_DMA in raid5 offload

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

This micro-optimization allowed the raid code to skip a re-read of the
parity block after checking parity.  It took advantage of the fact that
xor-offload-engines have their own internal result buffer and can check
parity without writing to memory.  Remove it for the following reasons:

1/ It is a layering violation for MD to need to manage the DMA and
   non-DMA paths within async_xor_zero_sum
2/ Bad precedent to toggle the 'ops' flags outside the lock
3/ Hard to realize a performance gain as reads will not need an updated
   parity block and writes will dirty it anyways.

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 08:31:50 +10:00 • committed by Neil Brown
parent 0cd17fec98
commit b203886edb
2 changed files with 0 additions and 12 deletions
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2
include/linux/raid/raid5.h
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@ -267,10 +267,8 @@ struct r6_state {
/* modifiers to the base operations
* STRIPE_OP_MOD_REPAIR_PD - compute the parity block and write it back
* STRIPE_OP_MOD_DMA_CHECK - parity is not corrupted by the check
*/
#define STRIPE_OP_MOD_REPAIR_PD 7
#define STRIPE_OP_MOD_DMA_CHECK 8
/*
* Plugging: