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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 23 Nov 2018 10:44:22 -0800
Message-ID: <CAHk-=wgpmV2B=s2xE5385Jzy2tEZuiW+MSPveJBfpqUoFdGydg@mail.gmail.com>
Subject: Re: [PATCH] x86: only use ERMS for user copies for larger sizes
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     David.Laight@aculab.com, Andrew Lutomirski <luto@kernel.org>,
        dvlasenk@redhat.com, Jens Axboe <axboe@kernel.dk>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, bp@alien8.de,
        Peter Anvin <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, brgerst@gmail.com,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        pabeni@redhat.com
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On Fri, Nov 23, 2018 at 10:39 AM Andy Lutomirski <luto@amacapital.net> wrot=
e:
>
> What is memcpy_to_io even supposed to do?  I=E2=80=99m guessing it=E2=80=
=99s defined as something like =E2=80=9Ccopy this data to IO space using at=
 most long-sized writes, all aligned, and writing each byte exactly once, i=
n order.=E2=80=9D  That sounds... dubiously useful.

We've got hundreds of users of it, so it's fairly common..

> I could see a function that writes to aligned memory in specified-sized c=
hunks.

We have that. It's called "__iowrite{32,64}_copy()". It has very few users.

                  Linus