Can you elaborate on which CPUs and with what workloads you measured that?
The kernel memcpy is optimized for copies smaller than a page size
for example (kernel very rarely does anything on larger than 4k),
the glibc isn't. etc. There are various other differences.
memcpy and memmove are very different. AFAIK noone has tried
to optimize memmove() before because traditionally it wasn't
used for anything performance critical in the kernel. Has that
that changed? memcpy on the other hand while not perfect
is actually quite optimized for typical workloads.
One big difference between the kernel and glibc is that kernel
is often cache cold, so you e.g. the cost of a very large code footprint
memcpy/memset is harder to amortize.
Microbenchmarks often leave out that crucial variable.
I have some systemtap scripts to measure size/alignment distributions of
copies on a kernel, if you have a particular workload you're interested
in those could be tried.
Just copying the glibc bloat uncritical is very likely
the wrong move at least.
-Andi
--
ak@linux.intel.com -- Speaking for myself only.
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