|author||Bob Pearson <firstname.lastname@example.org>||2012-03-23 15:02:21 -0700|
|committer||Linus Torvalds <email@example.com>||2012-03-23 16:58:37 -0700|
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: http://goo.gl/sgt3i ; 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 [firstname.lastname@example.org: changelog tweaks] Signed-off-by: Bob Pearson <email@example.com> Signed-off-by: Darrick J. Wong <firstname.lastname@example.org> Signed-off-by: Andrew Morton <email@example.com> Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
2 files changed, 2 insertions, 2 deletions
diff --git a/lib/crc32.c b/lib/crc32.c
index 4b35d2b4437c..ffea0c99a1f3 100644
@@ -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
diff --git a/lib/crc32defs.h b/lib/crc32defs.h
index 9b6773d73749..f5a540176571 100644
@@ -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 */
# define CRC_LE_BITS 8