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

Ben Dooks ben.dooks at codethink.co.uk
Tue Jun 22 10:45:37 PDT 2021

On 22/06/2021 13:05, Akira Tsukamoto wrote:
> On 6/22/2021 5:30 PM, Ben Dooks wrote:
>> 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?
> Thanks for the result on the Unmatched with hdparm. Have you tried
> iperf3?

I will see if there is iperf3 installed. I've not done much other than
try booting it and then try booting it with a kernel i've built from

> The 15% is high, is it before or with-patch?

Can't remember, I did this more to find out if the copy to/from user
was going to show up in the times for hdparm.

> Akira

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


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