From: Matteo Croce > Sent: 15 June 2021 03:38 > > Write a C version of memcpy() which uses the biggest data size allowed, > without generating unaligned accesses. I'm surprised that the C loop: > + for (; count >= bytes_long; count -= bytes_long) > + *d.ulong++ = *s.ulong++; ends up being faster than the ASM 'read lots' - 'write lots' loop. Especially since there was an earlier patch to convert copy_to/from_user() to use the ASM 'read lots' - 'write lots' loop instead of a tight single register copy loop. I'd also guess that the performance needs to be measured on different classes of riscv cpu. A simple cpu will behave differently to one that can execute multiple instructions per clock. Any form of 'out of order' execution also changes things. The other big change is whether the cpu can to a memory read and write in the same clock. I'd guess that riscv exist with some/all of those features. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
