On Fri, 4 Nov 2016 11:12:48 +1100 Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Fri, Oct 28, 2016 at 03:17:47AM +1100, Nicholas Piggin wrote: > > Hi guys, > > > > We're seeing crc32c_le show up in xfs log checksumming on a MySQL benchmark > > on powerpc. I could reproduce similar overheads with dbench as well. > > > > 1.11% mysqld [kernel.vmlinux] [k] __crc32c_le > > | > > ---__crc32c_le > > | > > --1.11%--chksum_update > > | > > --1.11%--crypto_shash_update > > crc32c > > xlog_cksum > > xlog_sync > > _xfs_log_force_lsn > > xfs_file_fsync > > vfs_fsync_range > > do_fsync > > sys_fsync > > system_call > > 0x17738 > > 0x17704 > > os_file_flush_func > > fil_flush > > > > As a rule, it helps the crc implementation if it can operate on as large a > > chunk as possible (alignment, startup overhead, etc). So I did a quick hack > > at getting XFS checksumming to feed crc32c() with larger chunks, by setting > > the existing crc to 0 before running over the entire buffer. Together with > > some small work on the powerpc crc implementation, crc drops below 0.1%. > > > > I don't know if something like this would be acceptable? It's not pretty, > > but I didn't see an easier way. > > Here's an alternative, slightly cleaner patch that optimises the CRC > update side but leaves the verify side as it is. I've not yet > decided exactly what is cleanest for the xlog_cksum() call in log > recovery, but that won't change the performance of the code. Can > you give this a run through, Nick? Hi Dave, Yeah sorry for the slow response, I've been getting a more realistic MySQL benchmark setup working (what I had reproduced what appeared to be the same overhead, but I wanted to get something better to retest with). So your patch comes at a good time (and thanks for working on it). I'll see if I can get something running and have results for you by next week. Thanks, Nick -- 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
