> -----Original Message----- > From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel- > owner@xxxxxxxxxxxxxxx] On Behalf Of Daniel Swarbrick > Sent: Monday, June 29, 2015 1:31 PM > > Yes, we have our own CRC32 checksum because loooong ago (before I > > started!) Sage saw a lot of network corruption that wasn't being > > caught by the TCP checksums so he added some to the Ceph message > > stream. I can't tell you with any authority whatsoever how common that > > problem is, but I don't think we're turning them off by default in > > upstream. :) > > If the CRC32 implementation in Ceph is that dated (particularly the software > implementations that will be used on AMD hardware), would it be worth > checking out some of the updated implementations, such as the > slice-by-16 or chunked methods? > I found this link http://create.stephan-brumme.com/crc32/ and tried running > the benchmark on an AMD Opteron 6386 SE system, with the following > results: First of all, this processor actually supports SSE 4.2. See here: http://www.cpu-world.com/CPUs/Bulldozer/AMD-Opteron%206386%20SE%20-%20OS6386YETGGHK.html In other words, it *does* support hardware CRC32 calculation. > bitwise : CRC=221F390F, 47.525s, 21.546 MB/s > half-byte : CRC=221F390F, 11.828s, 86.576 MB/s > 1 byte at once: CRC=221F390F, 6.347s, 161.332 MB/s > 4 bytes at once: CRC=221F390F, 2.875s, 356.178 MB/s > 8 bytes at once: CRC=221F390F, 2.004s, 510.932 MB/s > 4x8 bytes at once: CRC=221F390F, 1.929s, 530.811 MB/s > 16 bytes at once: CRC=221F390F, 1.892s, 541.179 MB/s > 16 bytes at once: CRC=221F390F, 1.926s, 531.797 MB/s (including > prefetching) > chunked : CRC=221F390F, 1.919s, 533.656 MB/s > > AFAIK, Ceph uses the slice-by-8 method if no hardware crc32 is found. Slicing-by-16 makes use of large (16k contrary to 8k used by slicing-by-8) so switching to slicing-by-16 would cause more cache trashing than with slicing-by-8 and in turn, decrease overall Ceph performance. Not to mention that in your case, slicing-by-16 was just ~31MB/s faster, which is just 6% faster. IMHO, increased memory usage is definitely not worth it. With best regards / Pozdrawiam Piotr Dałek ��.n��������+%������w��{.n����z��u���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
