linux-kernel - [PATCH] PM: align buffers for LZO compression

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Date:	Fri, 22 Feb 2013 08:46:31 +0100
From:	"Markus F.X.J. Oberhumer" <markus@...rhumer.com>
To:	Bojan Smojver <bojan@...ursive.com>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] PM: align buffers for LZO compression

Hi,

for performance reasons I'd strongly suggest that you explicitly align all
buffers passed to the LZO compress and decompress functions.

Below is a small (and completely untested!) patch, but I think you
get the idea.

BTW, it might be even more beneficial (esp. for NUMA systems) to align *all*
individual unc/cmp/wrk pointers to a multiple of the PAGE_SIZE, but this would
require some code restructuring.

Cheers,
Markus

completely untested patch:

diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 7c33ed2..7af4293 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -532,9 +532,9 @@ struct cmp_data {
        wait_queue_head_t done;                   /* compression done */
        size_t unc_len;                           /* uncompressed length */
        size_t cmp_len;                           /* compressed length */
-       unsigned char unc[LZO_UNC_SIZE];          /* uncompressed buffer */
-       unsigned char cmp[LZO_CMP_SIZE];          /* compressed buffer */
-       unsigned char wrk[LZO1X_1_MEM_COMPRESS];  /* compression workspace */
+       unsigned char unc[LZO_UNC_SIZE]         ____cacheline_aligned; /* uncompressed buffer */
+       unsigned char cmp[LZO_CMP_SIZE]         ____cacheline_aligned; /* compressed buffer */
+       unsigned char wrk[LZO1X_1_MEM_COMPRESS] ____cacheline_aligned; /* compression workspace */
 };

 /**
@@ -1021,8 +1021,8 @@ struct dec_data {
        wait_queue_head_t done;                   /* decompression done */
        size_t unc_len;                           /* uncompressed length */
        size_t cmp_len;                           /* compressed length */
-       unsigned char unc[LZO_UNC_SIZE];          /* uncompressed buffer */
-       unsigned char cmp[LZO_CMP_SIZE];          /* compressed buffer */
+       unsigned char unc[LZO_UNC_SIZE]         ____cacheline_aligned; /* uncompressed buffer */
+       unsigned char cmp[LZO_CMP_SIZE]         ____cacheline_aligned; /* compressed buffer */
 };

 /**


Signed-off-by: Markus F.X.J. Oberhumer <markus@...rhumer.com>

-- 
Markus Oberhumer, <markus@...rhumer.com>, http://www.oberhumer.com/
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