linux-kernel - [PATCH] lib/crc32: slice by 4 is more efficient than the default slice by 8 on Powerpc 8xx.

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Date:	Mon, 18 Nov 2013 08:04:23 +0100 (CET)
From:	Christophe Leroy <christophe.leroy@....fr>
To:	Vitaly Bordug <vitb@...nel.crashing.org>,
	Marcelo Tosatti <marcelo@...ck.org>,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	Bob Pearson <rpearson@...temfabricworks.com>
CC:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] lib/crc32: slice by 4 is more efficient than the default slice by 8 on Powerpc 8xx.

On PPC_8xx, CRC32_SLICEBY4 is more efficient (almost twice) than CRC32_SLICEBY8,
as shown below:

With CRC32_SLICEBY8:
[    1.109204] crc32: CRC_LE_BITS = 64, CRC_BE BITS = 64
[    1.114401] crc32: self tests passed, processed 225944 bytes in 15118910 nsec
[    1.130655] crc32c: CRC_LE_BITS = 64
[    1.134235] crc32c: self tests passed, processed 225944 bytes in 4479879 nsec

With CRC32_SLICEBY4:
[    1.097129] crc32: CRC_LE_BITS = 32, CRC_BE BITS = 32
[    1.101878] crc32: self tests passed, processed 225944 bytes in 8616242 nsec
[    1.116298] crc32c: CRC_LE_BITS = 32
[    1.119607] crc32c: self tests passed, processed 225944 bytes in 3289576 nsec

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Index: a/lib/Kconfig
===================================================================
--- a/lib/Kconfig	(révision 5325)
+++ b/lib/Kconfig	(copie de travail)
@@ -102,6 +102,7 @@
 choice
 	prompt "CRC32 implementation"
 	depends on CRC32
+	default CRC32_SLICEBY4 if PPC_8xx
 	default CRC32_SLICEBY8
 	help
 	  This option allows a kernel builder to override the default choice
--
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