On Fri, Jul 2, 2021 at 4:37 PM Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> wrote: > > On 02/07/2021 13:31, Matteo Croce wrote: > > From: Matteo Croce <mcroce@xxxxxxxxxxxxx> > > > > Rewrite the generic memcpy() to copy a word at time, without generating > > unaligned accesses. > > > > The procedure is made of three steps: > > First copy data one byte at time until the destination buffer is aligned > > to a long boundary. > > Then copy the data one long at time shifting the current and the next long > > to compose a long at every cycle. > > Finally, copy the remainder one byte at time. > > > > This is the improvement on RISC-V: > > > > original aligned: 75 Mb/s > > original unaligned: 75 Mb/s > > new aligned: 114 Mb/s > > new unaligned: 107 Mb/s > > > > and this the binary size increase according to bloat-o-meter: > > > > Function old new delta > > memcpy 36 324 +288 > > > > > > Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxxxxx> > > --- > > lib/string.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 77 insertions(+), 3 deletions(-) > > Doesn't arch/riscv/lib/memcpy.S also exist for an architecture > optimised version? I would have thought the lib/string.c version > was not being used? > > Yes, but this series started as C replacement for the assembly one, which generates unaligned accesses. Unfortunately the existing RISC-V processors can't handle unaligned accesses, so they are emulated with a terrible slowdown. Then, since there wasn't any riscv specific code, it was proposed as generic code: Discussion: https://lore.kernel.org/linux-riscv/20210617152754.17960-1-mcroce@xxxxxxxxxxxxxxxxxxx/ -- per aspera ad upstream
