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References: <cover.1452297867.git.tony.luck@intel.com> <19f6403f2b04d3448ed2ac958e656645d8b6e70c.1452297867.git.tony.luck@intel.com>
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From: Andy Lutomirski <luto@amacapital.net>
Date: Sat, 9 Jan 2016 09:57:25 -0800
Message-ID: <CALCETrVQ_NxcnDr4N-VqROrMJ2hUzMKgmxjxAZu9TFbznqSDcg@mail.gmail.com>
Subject: Re: [PATCH v8 3/3] x86, mce: Add __mcsafe_copy()
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To: Tony Luck <tony.luck@gmail.com>
Cc: linux-nvdimm <linux-nvdimm@ml01.01.org>, Dan Williams <dan.j.williams@intel.com>, Borislav Petkov <bp@alien8.de>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Robert <elliott@hpe.com>, Ingo Molnar <mingo@kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, X86 ML <x86@kernel.org>

On Sat, Jan 9, 2016 at 9:48 AM, Tony Luck <tony.luck@gmail.com> wrote:
> On Fri, Jan 8, 2016 at 5:49 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> On Jan 8, 2016 4:19 PM, "Tony Luck" <tony.luck@intel.com> wrote:
>>>
>>> Make use of the EXTABLE_FAULT exception table entries. This routine
>>> returns a structure to indicate the result of the copy:
>>
>> Perhaps this is silly, but could we make this feature depend on ERMS
>> and thus make the code a lot simpler?
>
> ERMS?

It's the fast string extension, aka Enhanced REP MOV STOS.  On CPUs
with that feature (and not disabled via MSR), plain ol' rep movs is
the fastest way to copy bytes.  I think this includes all Intel CPUs
from SNB onwards.

--Andy

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