From: Akira Tsukamoto <akira.tsukamoto@gmail.com>
To: Palmer Dabbelt <palmer@dabbelt.com>,
Guenter Roeck <linux@roeck-us.net>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Qiu Wenbo <qiuwenbo@kylinos.com.cn>,
Paul Walmsley <paul.walmsley@sifive.com>,
Albert Ou <aou@eecs.berkeley.edu>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 0/1] riscv: improving uaccess with logs from network bench
Date: Mon, 19 Jul 2021 23:55:01 +0900 [thread overview]
Message-ID: <afac7502-5de9-1fec-10c7-03dbb06a3f67@gmail.com> (raw)
In-Reply-To: <a7a801d2-13d2-7b5b-66a5-98e7c95b00cc@gmail.com>
Hi Palmer,
Please do not bather with this patch.
It still have bug for rv32 reported by Guenter and I will regenerate the
patch against v5.14-rc* since I made the patch against v5.13.x for this
patch.
Akira
On 7/19/2021 9:51 PM, Akira Tsukamoto wrote:
> Hi Guenter, Geert and Qiu,
>
> I fixed the bug which was overrunning the copy when the size was in the
> between 8*SZREG to 9*SZREG. The SZREG holds the bytes per register size
> which is 4 for RV32 and 8 for RV64.
>
> Do you mind trying this patch? It works OK at my place.
>
> Since I had to respin the patch I added word copy without unrolling when
> the size is in the between 2*SZREG to 9*SZREG to reduce the number of byte
> copies which has heavy overhead as Palmer has mentioned when he included
> this patch to riscv/for-next.
>
>
> I rewrote the functions but heavily influenced by Garry's memcpy
> function [1]. It must be written in assembler to handle page faults
> manually inside the function unlike other memcpy functions.
>
> This patch will reduce cpu usage dramatically in kernel space especially
> for applications which use sys-call with large buffer size, such as network
> applications. The main reason behind this is that every unaligned memory
> access will raise exceptions and switch between s-mode and m-mode causing
> large overhead.
>
> ---
> v3 -> v4:
> - Fixed overrun copy
> - Added word copy without unrolling to reduce byte copy for left over
>
> v2 -> v3:
> - Merged all patches
>
> v1 -> v2:
> - Added shift copy
> - Separated patches for readability of changes in assembler
> - Using perf results
>
> [1] https://lkml.org/lkml/2021/2/16/778
>
> Akira Tsukamoto (1):
> riscv: __asm_copy_to-from_user: Optimize unaligned memory access and
> pipeline stall
>
> arch/riscv/lib/uaccess.S | 218 ++++++++++++++++++++++++++++++++-------
> 1 file changed, 183 insertions(+), 35 deletions(-)
>
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prev parent reply other threads:[~2021-07-19 14:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-19 12:51 [PATCH v4 0/1] riscv: improving uaccess with logs from network bench Akira Tsukamoto
2021-07-19 12:53 ` [PATCH v4 1/1] riscv: __asm_copy_to-from_user: Optimize unaligned memory access and pipeline stall Akira Tsukamoto
2021-07-19 13:51 ` Guenter Roeck
2021-07-19 14:00 ` Akira Tsukamoto
2021-07-19 14:24 ` Guenter Roeck
2021-07-19 14:49 ` Akira Tsukamoto
2021-07-19 15:16 ` Guenter Roeck
2021-07-20 6:54 ` Akira Tsukamoto
2021-07-19 14:49 ` Geert Uytterhoeven
2021-07-19 15:22 ` Akira Tsukamoto
2021-07-19 14:55 ` Akira Tsukamoto [this message]
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