The generic memset reads dczid_el0 on every memset. This has a
significant impact on falkor for a range of sizes because reading
dczid_el0 is slow.
The DZP bit in the dczid_el0 register does not change dynamically, so
it is safe to read once during program startup. With this patch
dczid_el0 is read once during startup and zva_size is cached. This is
used to invoke the falkor-specific memset; the generic memset routine
remains unchanged.
The gains due to this are significant for falkor, with run time
reductions as high as 48%. Here's a sample from the falkor tests:
* sysdeps/aarch64/memset-reg.h: New file.
* sysdeps/aarch64/memset.S: Use it.
(__memset): Rename to MEMSET macro.
[ZVA_MACRO]: Use zva_macro.
* sysdeps/aarch64/multiarch/Makefile (sysdep_routines):
Add memset_generic and memset_falkor.
* sysdeps/aarch64/multiarch/ifunc-impl-list.c
(__libc_ifunc_impl_list): Add memset ifuncs.
* sysdeps/aarch64/multiarch/init-arch.h (INIT_ARCH): New
local variable zva_size.
* sysdeps/aarch64/multiarch/memset.c: New file.
* sysdeps/aarch64/multiarch/memset_generic.S: New file.
* sysdeps/aarch64/multiarch/memset_falkor.S: New file.
* sysdeps/aarch64/multiarch/rtld-memset.S: New file.
* sysdeps/unix/sysv/linux/aarch64/cpu-features.c
(DCZID_DZP_MASK): New macro.
(DCZID_BS_MASK): Likewise.
(init_cpu_features): Read and set zva_size.
* sysdeps/unix/sysv/linux/aarch64/cpu-features.h
(struct cpu_features): New member zva_size.