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

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Date:   Sat, 24 Jun 2023 18:22:19 +0800
From:   Yangyu Chen <cyy@...self.name>
To:     evan@...osinc.com
Cc:     ajones@...tanamicro.com, alexghiti@...osinc.com,
        andy.chiu@...ive.com, aou@...s.berkeley.edu,
        apatel@...tanamicro.com, conor.dooley@...rochip.com,
        corbet@....net, cyy@...self.name, 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

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

Thanks,
Yangyu Chen