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Commit b203886e authored by Dan Williams's avatar Dan Williams Committed by Neil Brown
Browse files

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: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarNeil Brown <neilb@suse.de>
parent 0cd17fec

drivers/md/raid5.c

+0 −10
Original line number Diff line number Diff line
@@ -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);

include/linux/raid/raid5.h

+0 −2
Original line number Diff line number Diff line
@@ -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: