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

[Ben Dooks]

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
upstream.

> 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


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

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