linux-kernel - [38/98] raid6: fix recovery performance regression

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Message-Id: <20100510223537.829202297@kvm.kroah.org>
Date:	Mon, 10 May 2010 15:34:50 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	NeilBrown <neilb@...e.de>,
	Dan Williams <dan.j.williams@...el.com>
Subject: [38/98] raid6: fix recovery performance regression

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Dan Williams <dan.j.williams@...el.com>

commit 5157b4aa5b7de8787b6318e61bcc285031bb9088 upstream.

The raid6 recovery code should immediately drop back to the optimized
synchronous path when a p+q dma resource is not available.  Otherwise we
run the non-optimized/multi-pass async code in sync mode.

Verified with raid6test (NDISKS=255)

Applies to kernels >= 2.6.32.

Acked-by: NeilBrown <neilb@...e.de>
Reported-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 crypto/async_tx/async_raid6_recov.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

--- a/crypto/async_tx/async_raid6_recov.c
+++ b/crypto/async_tx/async_raid6_recov.c
@@ -324,6 +324,7 @@ struct dma_async_tx_descriptor *
 async_raid6_2data_recov(int disks, size_t bytes, int faila, int failb,
 			struct page **blocks, struct async_submit_ctl *submit)
 {
+	void *scribble = submit->scribble;
 	int non_zero_srcs, i;
 
 	BUG_ON(faila == failb);
@@ -332,11 +333,13 @@ async_raid6_2data_recov(int disks, size_
 
 	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);
 
-	/* we need to preserve the contents of 'blocks' for the async
-	 * case, so punt to synchronous if a scribble buffer is not available
+	/* if a dma resource is not available or a scribble buffer is not
+	 * available punt to the synchronous path.  In the 'dma not
+	 * available' case be sure to use the scribble buffer to
+	 * preserve the content of 'blocks' as the caller intended.
 	 */
-	if (!submit->scribble) {
-		void **ptrs = (void **) blocks;
+	if (!async_dma_find_channel(DMA_PQ) || !scribble) {
+		void **ptrs = scribble ? scribble : (void **) blocks;
 
 		async_tx_quiesce(&submit->depend_tx);
 		for (i = 0; i < disks; i++)
@@ -406,11 +409,13 @@ async_raid6_datap_recov(int disks, size_
 
 	pr_debug("%s: disks: %d len: %zu\n", __func__, disks, bytes);
 
-	/* we need to preserve the contents of 'blocks' for the async
-	 * case, so punt to synchronous if a scribble buffer is not available
+	/* if a dma resource is not available or a scribble buffer is not
+	 * available punt to the synchronous path.  In the 'dma not
+	 * available' case be sure to use the scribble buffer to
+	 * preserve the content of 'blocks' as the caller intended.
 	 */
-	if (!scribble) {
-		void **ptrs = (void **) blocks;
+	if (!async_dma_find_channel(DMA_PQ) || !scribble) {
+		void **ptrs = scribble ? scribble : (void **) blocks;
 
 		async_tx_quiesce(&submit->depend_tx);
 		for (i = 0; i < disks; i++)


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