From: Bin Meng <bmeng.cn@gmail.com>
To: David Laight <David.Laight@aculab.com>, Gary Guo <gary@garyguo.net>
Cc: Matteo Croce <mcroce@linux.microsoft.com>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Atish Patra <atish.patra@wdc.com>,
Emil Renner Berthing <kernel@esmil.dk>,
Akira Tsukamoto <akira.tsukamoto@gmail.com>,
Drew Fustini <drew@beagleboard.org>
Subject: Re: [PATCH 1/3] riscv: optimized memcpy
Date: Tue, 15 Jun 2021 21:28:57 +0800 [thread overview]
Message-ID: <CAEUhbmU0cPkawmFfDd_sPQnc9V-cfYd32BCQo4Cis3uBKZDpXw@mail.gmail.com> (raw)
In-Reply-To: <1632006872b04c64be828fa0c4e4eae0@AcuMS.aculab.com>
On Tue, Jun 15, 2021 at 9:18 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Bin Meng
> > Sent: 15 June 2021 14:09
> >
> > On Tue, Jun 15, 2021 at 4:57 PM David Laight <David.Laight@aculab.com> wrote:
> > >
> ...
> > > I'm surprised that the C loop:
> > >
> > > > + for (; count >= bytes_long; count -= bytes_long)
> > > > + *d.ulong++ = *s.ulong++;
> > >
> > > ends up being faster than the ASM 'read lots' - 'write lots' loop.
> >
> > I believe that's because the assembly version has some unaligned
> > access cases, which end up being trap-n-emulated in the OpenSBI
> > firmware, and that is a big overhead.
>
> Ah, that would make sense since the asm user copy code
> was broken for misaligned copies.
> I suspect memcpy() was broken the same way.
>
Yes, Gary Guo sent one patch long time ago against the broken assembly
version, but that patch was still not applied as of today.
https://patchwork.kernel.org/project/linux-riscv/patch/20210216225555.4976-1-gary@garyguo.net/
I suggest Matteo re-test using Gary's version.
> I'm surprised IP_NET_ALIGN isn't set to 2 to try to
> avoid all these misaligned copies in the network stack.
> Although avoiding 8n+4 aligned data is rather harder.
>
> Misaligned copies are just best avoided - really even on x86.
> The 'real fun' is when the access crosses TLB boundaries.
Regards,
Bin
next prev parent reply other threads:[~2021-06-15 13:29 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-15 2:38 [PATCH 0/3] riscv: optimized mem* functions Matteo Croce
2021-06-15 2:38 ` [PATCH 1/3] riscv: optimized memcpy Matteo Croce
2021-06-15 8:57 ` David Laight
2021-06-15 13:08 ` Bin Meng
2021-06-15 13:18 ` David Laight
2021-06-15 13:28 ` Bin Meng [this message]
2021-06-15 16:12 ` Emil Renner Berthing
2021-06-16 0:33 ` Bin Meng
2021-06-16 2:01 ` Matteo Croce
2021-06-16 8:24 ` David Laight
2021-06-16 10:48 ` Akira Tsukamoto
2021-06-16 19:06 ` Matteo Croce
2021-06-15 13:44 ` Matteo Croce
2021-06-16 11:46 ` Guo Ren
2021-06-16 18:52 ` Matteo Croce
2021-06-17 21:30 ` David Laight
2021-06-17 21:48 ` Matteo Croce
2021-06-18 0:32 ` Matteo Croce
2021-06-18 1:05 ` Matteo Croce
2021-06-18 8:32 ` David Laight
2021-06-15 2:38 ` [PATCH 2/3] riscv: optimized memmove Matteo Croce
2021-06-15 2:38 ` [PATCH 3/3] riscv: optimized memset Matteo Croce
2021-06-15 2:43 ` [PATCH 0/3] riscv: optimized mem* functions Bin Meng
2024-01-28 11:10 [PATCH 0/3] riscv: optimize memcpy/memmove/memset Jisheng Zhang
2024-01-28 11:10 ` [PATCH 1/3] riscv: optimized memcpy Jisheng Zhang
2024-01-28 12:35 ` David Laight
2024-01-30 12:11 ` Nick Kossifidis
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