On Fri, Aug 23, 2019 at 09:43:22AM +0000, Paul Jones wrote: > > > Am Do., 22. Aug. 2019 um 16:41 Uhr schrieb Holger Hoffstätte > > > <hol...@applied-asynchrony.com>: > > > > but how does btrfs benefit from this compared to using crc32-intel? > > > > > > As i know, crc32c is as far as ~3x faster than xxhash. But xxHash was > > > created with a differend design goal. > > > If you using a cpu without hardware crc32 support, xxHash provides you > > > a maximum portability and speed. Look at arm, mips, power, etc. or old > > > intel cpus like Core 2 Duo. > > > > I've got a modified version of smhasher > > (https://github.com/PeeJay/smhasher) that tests speed and cryptographics > > of various hashing functions. > > I forgot to add xxhash32 > > Crc32 Software - 379.91 MiB/sec > Crc32 Hardware - 7338.60 MiB/sec > XXhash64 Software - 12094.40 MiB/sec > XXhash32 Software - 6060.11 MiB/sec > > Testing done on a 1st Gen Ryzen. Impressive numbers from XXhash64.
Newest biggest Threadripper (2990WX, no 3* version released yet): crc32 - 492.75 MiB/sec crc32hw - 9447.37 MiB/sec crc64 - 1959.51 MiB/sec xxhash32 - 7479.29 MiB/sec xxhash64 - 14911.58 MiB/sec An old Skylake (i7-6700): crc32 - 359.32 MiB/sec crc32hw - 21119.68 MiB/sec crc64 - 1656.34 MiB/sec xxhash32 - 5989.87 MiB/sec xxhash64 - 11949.41 MiB/sec Cascade Lake (0000%@): crc32hw 1.92× as fast as xxhash64. So you want crc32hw on Intel, xxhash64 on AMD. crc32 also allows going back to old kernels; the improved collision resistance of xxhash64 is not a reason as if you intend to dedupe you want a crypto hash so you don't need to verify. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ ⢿⡄⠘⠷⠚⠋ The root of a real enemy is an imaginary friend. ⠈⠳⣄⠀⠀⠀⠀
