From: Coly Li > Sent: 17 July 2018 15:55 > > This patch adds the re-write crc64 calculation routines for Linux kernel. > The CRC64 polynomical arithmetic follows ECMA-182 specification, inspired > by CRC paper of Dr. Ross N. Williams > (see http://www.ross.net/crc/download/crc_v3.txt) and other public domain > implementations. > > All the changes work in this way, > - When Linux kernel is built, host program lib/gen_crc64table.c will be > compiled to lib/gen_crc64table and executed. That seems excessive for a fixed table. No real point doing more than putting a commented out copy of the code with the initialisation data. > - The output of gen_crc64table execution is an array called as lookup > table (a.k.a POLY 0x42f0e1eba9ea369) which contain 256 64bits-long > numbers, this talbe is dumped into header file lib/crc64table.h. > - Then the header file is included by lib/crc64.c for normal 64bit crc > calculation. How long are the buffers being processed? For short buffers a lot of bytes will suffer cache line misses. For longer buffers you'll be displacing 2k of data from the L1 data cache. That could easily have a knock on effect on the surrounding code. You might find that a nibble based loop and lookup table is faster. Or, relying on the linearity of CRCs, separate lookup tables for the high and low nibbles of each byte. So replacing: crc = crc64table[t] ^ (crc << 8); with: crc = crc64table_hi[t >> 4] ^ crc64table_lo[t & 15] ^ (crc << 8); David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
