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>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 8c4e614..60e61d2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -837,15 +837,10 @@
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 @@
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);
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index f0827d3..4ecae31 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -267,10 +267,8 @@
/* 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: