Commit e30c7a8f authored by Bob Pearson's avatar Bob Pearson Committed by Linus Torvalds

crc32: remove two instances of trailing whitespaces

This patchset (re)uses Bob Pearson's crc32 slice-by-8 code to stamp out
a software crc32c implementation.  It removes the crc32c implementation
in crypto/ in favor of using the stamped-out one in lib/.  There is also
a change to Kconfig so that the kernel builder can pick an
implementation best suited for the hardware.

The motivation for this patchset is that I am working on adding full
metadata checksumming to ext4.  As far as performance impact of adding
checksumming goes, I see nearly no change with a standard mail server
ffsb simulation.  On a test that involves only file creation and
deletion and extent tree writes, I see a drop of about 50 pcercent with
the current kernel crc32c implementation; this improves to a drop of
about 20 percent with the enclosed crc32c code.

When metadata is usually a small fraction of total IO, this new
implementation doesn't help much because metadata is usually a small
fraction of total IO.  However, when we are doing IO that is almost all
metadata (such as rm -rf'ing a tree), then this patch speeds up the
operation substantially.

Incidentally, given that iscsi, sctp, and btrfs also use crc32c, this
patchset should improve their speed as well.  I have not yet quantified
that, however.  This latest submission combines Bob's patches from late
August 2011 with mine so that they can be one coherent patch set.
Please excuse my inability to combine some of the patches; I've been
advised to leave Bob's patches alone and build atop them instead.  :/

Since the last posting, I've also collected some crc32c test results on
a bunch of different x86/powerpc/sparc platforms.  The results can be
viewed here: ; the "crc32-kern-le" and "crc32c"
columns describe the performance of the kernel's current crc32 and
crc32c software implementations.  The "crc32c-by8-le" column shows
crc32c performance with this patchset applied.  I expect crc32
performance to be roughly the same.

The two _boost columns at the right side of the spreadsheet shows how much
faster the new implementation is over the old one.  As you can see, crc32
rises substantially, and crc32c experiences a huge increase.

This patch:

- remove trailing whitespace from lib/crc32.c
- remove trailing whitespace from lib/crc32defs.h

[ changelog tweaks]
Signed-off-by: default avatarBob Pearson <>
Signed-off-by: default avatarDarrick J. Wong <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent ca56dc09
......@@ -317,7 +317,7 @@ EXPORT_SYMBOL(crc32_be);
* in the correct multiple to subtract, we can shift a byte at a time.
* This produces a 40-bit (rather than a 33-bit) intermediate remainder,
* but again the multiple of the polynomial to subtract depends only on
* the high bits, the high 8 bits in this case.
* the high bits, the high 8 bits in this case.
* The multiple we need in that case is the low 32 bits of a 40-bit
* value whose high 8 bits are given, and which is a multiple of the
......@@ -8,7 +8,7 @@
/* How many bits at a time to use. Requires a table of 4<<CRC_xx_BITS bytes. */
/* For less performance-sensitive, use 4 */
#ifndef CRC_LE_BITS
#ifndef CRC_LE_BITS
# define CRC_LE_BITS 8
#ifndef CRC_BE_BITS
Markdown is supported
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment