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>

1 files changed, 0 insertions, 10 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 8c4e6149daea..60e61d2464b5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -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);