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

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Date:   Tue, 22 Jun 2021 21:05:27 +0900
From:   Akira Tsukamoto <akira.tsukamoto@...il.com>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>,
        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 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?

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

Akira