On Sat, May 13, 2017 at 12:33:44PM -0700, Darrick J. Wong wrote: > The crc32c code used in xfsprogs was copied directly from the Linux > kernel. However, that code selects slice-by-4 by default, which isn't > the fastest -- that's slice-by-8, which trades table size for speed. > Fix some makefile dependency problems and explicitly select the > algorithm we want. With this patch applied, I see about a 10% drop in > CPU time running xfs_repair. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > --- > libxfs/Makefile | 4 ++-- > libxfs/crc32defs.h | 3 +++ > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/libxfs/Makefile b/libxfs/Makefile > index 0f3759e..c5dc382 100644 > --- a/libxfs/Makefile > +++ b/libxfs/Makefile > @@ -124,7 +124,7 @@ LDIRT = gen_crc32table crc32table.h crc32selftest > > default: crc32selftest ltdepend $(LTLIBRARY) > > -crc32table.h: gen_crc32table.c > +crc32table.h: gen_crc32table.c crc32defs.h > @echo " [CC] gen_crc32table" > $(Q) $(BUILD_CC) $(BUILD_CFLAGS) -o gen_crc32table $< > @echo " [GENERATE] $@" > @@ -135,7 +135,7 @@ crc32table.h: gen_crc32table.c > # systems/architectures. Hence we make sure that xfsprogs will never use a > # busted CRC calculation at build time and hence avoid putting bad CRCs down on > # disk. > -crc32selftest: gen_crc32table.c crc32table.h crc32.c > +crc32selftest: gen_crc32table.c crc32table.h crc32.c crc32defs.h > @echo " [TEST] CRC32" > $(Q) $(BUILD_CC) $(BUILD_CFLAGS) -D CRC32_SELFTEST=1 crc32.c -o $@ > $(Q) ./$@ > diff --git a/libxfs/crc32defs.h b/libxfs/crc32defs.h > index 64cba2c..153f44c 100644 > --- a/libxfs/crc32defs.h > +++ b/libxfs/crc32defs.h > @@ -1,3 +1,6 @@ > +/* Use slice-by-8, which is the fastest variant. */ > +# define CRC_LE_BITS 64 I'm not sure this works on all platforms and builds, whereas the existing slice-by-4 default should work for them all, but may not be the fastest. This code in the crc32defs.h: #ifndef CRC_LE_BITS # ifdef CONFIG_64BIT # define CRC_LE_BITS 64 # else # define CRC_LE_BITS 32 # endif #endif kinda tells us what the "optimal" default should be. And keep in mind that the kernel has arch-specific settings: $ git grep CONFIG_CRC32_S arch/mips/configs/bcm47xx_defconfig:CONFIG_CRC32_SARWATE=y arch/mips/configs/db1xxx_defconfig:CONFIG_CRC32_SLICEBY4=y arch/mips/configs/rt305x_defconfig:CONFIG_CRC32_SARWATE=y arch/mips/configs/xway_defconfig:CONFIG_CRC32_SARWATE=y arch/powerpc/configs/adder875_defconfig:CONFIG_CRC32_SLICEBY4=y arch/powerpc/configs/ep88xc_defconfig:CONFIG_CRC32_SLICEBY4=y arch/powerpc/configs/mpc866_ads_defconfig:CONFIG_CRC32_SLICEBY4=y arch/powerpc/configs/mpc885_ads_defconfig:CONFIG_CRC32_SLICEBY4=y arch/powerpc/configs/tqm8xx_defconfig:CONFIG_CRC32_SLICEBY4=y .... Which says that certain mips and powerpc CPUs should be using slice-by-4 or sarwate algorithms, not slice-by-8.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
