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

Ben Dooks ben.dooks at codethink.co.uk
Tue Jun 22 01:30:26 PDT 2021

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

I did a quick test on a SiFive Unmatched with IO to an NVME.

before: cached-reads=172.47MB/sec, buffered-reads=135.8MB/sec
with-patch: cached-read=s177.54Mb/sec, buffered-reads=137.79MB/sec

That was just one test run, so there was a small improvement. I am
sort of surprised we didn't get more of a win from this.

perf record on hdparm shows that it spends approx 15% cpu time in
asm_copy_to_user. Does anyone have a benchmark for this which just
looks at copy/to user? if not should we create one?

Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius


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