Messages in this thread | | | Date | Wed, 23 Nov 2011 13:51:50 +0100 | From | "N. Coesel" <> | Subject | Re: Fast memcpy patch |
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Sasha,
At 13:10 23-11-2011, Sasha Levin wrote: >On Wed, 2011-11-23 at 12:25 +0100, N. Coesel wrote: > > Dear readers, > > I noticed the Linux kernel still uses a byte-by-byte copy method for > > memcpy. Since most memory allocations are aligned to the integer size > > of a cpu it is often faster to copy by using the CPU's native word > > size. The patch below does that. The code is already at work in many > > 16 and 32 bit embedded products. It should also work for 64 bit > > platforms. So far I only tested 16 and 32 bit platforms. > >[snip] > >memcpy (along with other mem* functions) are arch specific - for >example, look at arch/x86/lib/memcpy_64.S for the implementation(s) for >x86. > >The code under lib/string.c is simple and should work on all platforms >(and is probably not being used anywhere anymore).
Thanks for pointing that out. Currently my primary target is ARM. It seems the memcpy for that arch uses byte-by-byte copying as well with some loop unrolling. I modified the code so it tries to use word-by-word copy if the pointers are aligned on word boundaries, if not it reverts to the old method. For clarity: by word I mean the CPU's native bus width. In case of ARM that's (still) 32 bit.
Nico Coesel
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