[PATCH v2 0/5] riscv: improving uaccess with logs from network bench
Akira Tsukamoto
akira.tsukamoto at gmail.com
Sat Jun 19 04:21:17 PDT 2021
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
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