commit 8dc90c15e1cccd6d17dc056ada38aba8879c914f
Author: Markus Stockhausen <markus.stockhausen@xxxxxxxxxxx>
Date: Sun Aug 10 09:41:57 2014 +0000
async_pq: add logic for improved rmw syndrome calculation
raid5 uses async syndrome functions where possible. Adapt that
layer so we have a seamless integration of the new xor_syndrome()
calls. This is achieved by introducing the new submit flag
ASYNC_TX_PQ_XOR_DST. If it is active the caller wants to factor
in/out blocks of the syndrome.
For now we focus on the synchronous implementation as the DMA
assisted feature cannot be tested. The only known device to support
P/Q calculation is an IOP13XX. See arch/arm/mach-iop13xx/setup.c.
An implementation of the RAID6 rmw cycle will therefore always run
on the CPU.
The patch will determine the first and the last block within a
stripe that conatins changed data. These parameters are handed over
to xor_syndrome() that can avoid unneeded CPU cycles. To use this
feature the caller must fill NULL pointers for data pages that
won't change during a rmw run.
diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index d05327c..52922d8 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -124,6 +124,7 @@ do_sync_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
{
void **srcs;
int i;
+ int start = -1, stop = disks - 3;
if (submit->scribble)
srcs = submit->scribble;
@@ -134,10 +135,21 @@ do_sync_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
if (blocks[i] == NULL) {
BUG_ON(i > disks - 3); /* P or Q can't be zero */
srcs[i] = (void*)raid6_empty_zero_page;
- } else
+ } else {
srcs[i] = page_address(blocks[i]) + offset;
+ if (i < disks - 2) {
+ stop = i;
+ if (start == -1)
+ start = i;
+ }
+ }
}
- raid6_call.gen_syndrome(disks, len, srcs);
+ if (submit->flags & ASYNC_TX_PQ_XOR_DST) {
+ BUG_ON(!raid6_call.hasxor);
+ if (start >= 0)
+ raid6_call.xor_syndrome(disks, start, stop, len, srcs);
+ } else
+ raid6_call.gen_syndrome(disks, len, srcs);
async_tx_sync_epilog(submit);
}
@@ -178,7 +190,8 @@ async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
if (device)
unmap = dmaengine_get_unmap_data(device->dev, disks, GFP_NOIO);
- if (unmap &&
+ /* XORing P/Q is only implemented in software */
+ if (unmap && !(submit->flags & ASYNC_TX_PQ_XOR_DST) &&
(src_cnt <= dma_maxpq(device, 0) ||
dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
is_dma_pq_aligned(device, offset, 0, len)) {
diff --git a/include/linux/async_tx.h b/include/linux/async_tx.h
index 179b38f..388574e 100644
--- a/include/linux/async_tx.h
+++ b/include/linux/async_tx.h
@@ -60,12 +60,15 @@ struct dma_chan_ref {
* dependency chain
* @ASYNC_TX_FENCE: specify that the next operation in the dependency
* chain uses this operation's result as an input
+ * @ASYNC_TX_PQ_XOR_DST: do not overwrite the syndrome but XOR it with the
+ * input data. Required for rmw case.
*/
enum async_tx_flags {
ASYNC_TX_XOR_ZERO_DST = (1 << 0),
ASYNC_TX_XOR_DROP_DST = (1 << 1),
ASYNC_TX_ACK = (1 << 2),
ASYNC_TX_FENCE = (1 << 3),
+ ASYNC_TX_PQ_XOR_DST = (1 << 4),
};
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