linux-kernel - Re: [PATCH v8 3/3] x86, mce: Add __mcsafe

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Date:	Sat, 9 Jan 2016 09:57:25 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Tony Luck <tony.luck@...il.com>
Cc:	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert <elliott@....com>, Ingo Molnar <mingo@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v8 3/3] x86, mce: Add __mcsafe_copy()

On Sat, Jan 9, 2016 at 9:48 AM, Tony Luck <tony.luck@...il.com> wrote:
> On Fri, Jan 8, 2016 at 5:49 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Jan 8, 2016 4:19 PM, "Tony Luck" <tony.luck@...el.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