[PATCH v2 0/5] riscv: improving uaccess with logs from network bench

[Akira Tsukamoto]

Optimizing copy_to_user and copy_from_user.

I rewrote the functions in v2, heavily influenced by Garry's memcpy
function [1].
The functions must be written in assembler to handle page faults manually
inside the function.

With the changes, improves in the percentage usage and some performance
of network speed in UDP packets.
Only patching copy_user. Using the original memcpy.

All results are from the same base kernel, same rootfs and same
BeagleV beta board.

Comparison by "perf top -Ue task-clock" while running iperf3.

--- TCP recv ---
 * Before
  40.40%  [kernel]  [k] memcpy
  33.09%  [kernel]  [k] __asm_copy_to_user
 * After
  50.35%  [kernel]  [k] memcpy
  13.76%  [kernel]  [k] __asm_copy_to_user

--- TCP send ---
 * Before
  19.96%  [kernel]  [k] memcpy
   9.84%  [kernel]  [k] __asm_copy_to_user
 * After
  14.27%  [kernel]  [k] memcpy
   7.37%  [kernel]  [k] __asm_copy_to_user

--- UDP send ---
 * Before
  25.18%  [kernel]  [k] memcpy
  22.50%  [kernel]  [k] __asm_copy_to_user
 * After
  28.90%  [kernel]  [k] memcpy
   9.49%  [kernel]  [k] __asm_copy_to_user

--- UDP recv ---
 * Before
  44.45%  [kernel]  [k] memcpy
  31.04%  [kernel]  [k] __asm_copy_to_user
 * After
  55.62%  [kernel]  [k] memcpy
  11.22%  [kernel]  [k] __asm_copy_to_user

Processing network packets require a lot of unaligned access for the packet
header, which is not able to change the design of the header format to be
aligned.
And user applications call system calls with a large buffer for send/recf()
and sendto/recvfrom() to repeat less function calls for the optimization.

v1 -> v2:
- Added shift copy
- Separated patches for readability of changes in assembler
- Using perf results

[1] https://lkml.org/lkml/2021/2/16/778

Akira Tsukamoto (5):
  riscv: __asm_to/copy_from_user: delete existing code
  riscv: __asm_to/copy_from_user: Adding byte copy first
  riscv: __asm_to/copy_from_user: Copy until dst is aligned address
  riscv: __asm_to/copy_from_user: Bulk copy while shifting misaligned
    data
  riscv: __asm_to/copy_from_user: Bulk copy when both src dst are
    aligned

 arch/riscv/lib/uaccess.S | 181 +++++++++++++++++++++++++++++++--------
 1 file changed, 146 insertions(+), 35 deletions(-)

--
2.17.1