[PATCH 0/2] RISC-V: ifunced memcpy using new kernel hwprobe interface

[Evan Green]

This series illustrates the use of a proposed Linux syscall that
enumerates architectural information about the RISC-V cores the system
is running on. In this series we expose a small wrapper function around
the syscall. An ifunc selector for memcpy queries it to see if unaligned
access is "fast" on this hardware. If it is, it selects a newly provided
implementation of memcpy that doesn't work hard at aligning the src and
destination buffers.

This is somewhat of a proof of concept for the syscall itself, but I do
find that in my goofy  memcpy test [1], the unaligned memcpy performed at
least as well as the generic C version. This is however on Qemu on an M1
mac, so not a test of any real hardware (more a smoke test that the
implementation isn't silly).

v1 of the Linux series can be found at [2]. I'm about to post v2 (but
haven't yet!), I can reply here with the link once v2 is posted.

[1] https://pastebin.com/Nj8ixpkX
[2] https://yhbt.net/lore/all/20221013163551.6775-1-palmer@rivosinc.com/


Evan Green (2):
  riscv: Add Linux hwprobe syscall support
  riscv: Add and use alignment-ignorant memcpy

 sysdeps/riscv/memcopy.h                       |  28 +++++
 sysdeps/riscv/memcpy.c                        |  65 +++++++++++
 sysdeps/riscv/memcpy_noalignment.S            | 103 ++++++++++++++++++
 sysdeps/unix/sysv/linux/riscv/Makefile        |   8 +-
 sysdeps/unix/sysv/linux/riscv/Versions        |   3 +
 sysdeps/unix/sysv/linux/riscv/hwprobe.c       |  30 +++++
 .../unix/sysv/linux/riscv/memcpy-generic.c    |  24 ++++
 .../unix/sysv/linux/riscv/rv32/arch-syscall.h |   1 +
 .../unix/sysv/linux/riscv/rv32/libc.abilist   |   1 +
 .../unix/sysv/linux/riscv/rv64/arch-syscall.h |   1 +
 .../unix/sysv/linux/riscv/rv64/libc.abilist   |   1 +
 sysdeps/unix/sysv/linux/riscv/sys/hwprobe.h   |  34 ++++++
 sysdeps/unix/sysv/linux/syscall-names.list    |   1 +
 13 files changed, 298 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/riscv/memcopy.h
 create mode 100644 sysdeps/riscv/memcpy.c
 create mode 100644 sysdeps/riscv/memcpy_noalignment.S
 create mode 100644 sysdeps/unix/sysv/linux/riscv/hwprobe.c
 create mode 100644 sysdeps/unix/sysv/linux/riscv/memcpy-generic.c
 create mode 100644 sysdeps/unix/sysv/linux/riscv/sys/hwprobe.h

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2.25.1