Re: [PATCH v2 0/5] riscv: improving uaccess with logs from network bench
From: Ben Dooks <hidden>
Date: 2021-06-20 10:22:47
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lkml
On 19/06/2021 12:21, Akira Tsukamoto wrote:
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.
Is there a git tree for these to try them out?
quoted hunk ↗ jump to hunk
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
What's the memcpy figure in the above? Could you explain the figures please?
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.
Isn't there an option to allow padding of network packets in the skbuff to make the fields aligned for architectures which do not have efficient unaligned loads (looking at you arm32). Has this been looked at?
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(-)
I'm concerned that delete and then re-add is either going to make the series un-bisectable or leave a point where the kernel is very broken? -- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius https://www.codethink.co.uk/privacy.html _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv