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

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Date:   Tue, 22 Jun 2021 09:30:26 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     Akira Tsukamoto <akira.tsukamoto@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 0/5] riscv: improving uaccess with logs from network
 bench

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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