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md: kill STRIPE_OP_MOD_DMA in raid5 offload 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/md/raid5.c
View File

@ -837,15 +837,10 @@ ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx,
static void ops_complete_check(void *stripe_head_ref)
{
struct stripe_head *sh = stripe_head_ref;
int pd_idx = sh->pd_idx;
pr_debug("%s: stripe %llu\n", __func__,
(unsigned long long)sh->sector);
if (test_and_clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending) &&
sh->ops.zero_sum_result == 0)
set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
set_bit(STRIPE_OP_CHECK, &sh->ops.complete);
set_bit(STRIPE_HANDLE, &sh->state);
release_stripe(sh);
@ -873,11 +868,6 @@ static void ops_run_check(struct stripe_head *sh)
tx = async_xor_zero_sum(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
&sh->ops.zero_sum_result, 0, NULL, NULL, NULL);
if (tx)
set_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);
else
clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);
atomic_inc(&sh->count);
tx = async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
ops_complete_check, sh);

2
include/linux/raid/raid5.h
View File

@ -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: