linux-kernel - Re: [PATCH 0/2] RISC-V: Probe for misaligned access speed

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Message-ID: <CALs-Hsv+iS055GUJdotYxmn5ST9y9yT7P1PiG4DLPU+rzPO20A@mail.gmail.com>
Date:   Mon, 26 Jun 2023 12:48:42 -0700
From:   Evan Green <evan@...osinc.com>
To:     Yangyu Chen <cyy@...self.name>
Cc:     ajones@...tanamicro.com, alexghiti@...osinc.com,
        andy.chiu@...ive.com, aou@...s.berkeley.edu,
        apatel@...tanamicro.com, conor.dooley@...rochip.com,
        corbet@....net, greentime.hu@...ive.com, guoren@...nel.org,
        heiko.stuebner@...ll.eu, heiko@...ech.de,
        jeeheng.sia@...rfivetech.com, jszhang@...nel.org,
        leyfoon.tan@...rfivetech.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        lizhengyu3@...wei.com, masahiroy@...nel.org, palmer@...belt.com,
        palmer@...osinc.com, paul.walmsley@...ive.com,
        rdunlap@...radead.org, samuel@...lland.org, shosie@...osinc.com,
        sunilvl@...tanamicro.com, xianting.tian@...ux.alibaba.com
Subject: Re: [PATCH 0/2] RISC-V: Probe for misaligned access speed

On Sat, Jun 24, 2023 at 3:22 AM Yangyu Chen <cyy@...self.name> wrote:
>
> Hi,
>
> Thanks for doing this.
>
> On 6/24/23 6:20 AM, Evan Green wrote:
> > I don't have a machine where misaligned accesses are slow, but I'd be
> > interested to see the results of booting this series if someone did.
>
> I have tested your patches on a 100MHz BigCore rocket-chip with opensbi running on FPGA with 72bit(64bit+ECC) DDR3 1600MHz memory. As the rocket-chip did not support misaligned memory access, every misaligned memory access will trap and emulated by SBI.
>
> Here is the result:
>
> ~ # cat /proc/cpuinfo
> processor       : 0
> hart            : 0
> isa             : rv64imafdc
> mmu             : sv39
> uarch           : sifive,rocket0
> mvendorid       : 0x0
> marchid         : 0x1
> mimpid          : 0x20181004
>
> processor       : 1
> hart            : 1
> isa             : rv64imafdc
> mmu             : sv39
> uarch           : sifive,rocket0
> mvendorid       : 0x0
> marchid         : 0x1
> mimpid          : 0x20181004
>
> ~ # dmesg | grep Unaligned
> [    0.210140] cpu1: Unaligned word copy 0 MB/s, byte copy 38 MB/s, misaligned accesses are slow
> [    0.410715] cpu0: Unaligned word copy 0 MB/s, byte copy 35 MB/s, misaligned accesses are slow

Thank you, Yangyu! Oof, the firmware traps are quite slow!
-Evan