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Subject: Re: [PATCH v2 0/5] riscv: improving uaccess with logs from network
 bench
To:     Ben Dooks <ben.dooks@codethink.co.uk>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
References: <5a5c07ac-8c11-79d3-46a3-a255d4148f76@gmail.com>
 <e7d5f98b-5e0d-19b3-08f5-a7b49d542a85@codethink.co.uk>
From:   Akira Tsukamoto <akira.tsukamoto@gmail.com>
Message-ID: <f54ec904-2bf5-0c29-d467-7465993d5d6b@gmail.com>
Date:   Tue, 22 Jun 2021 21:05:27 +0900
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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