Re: [PATCH v8 3/3] x86, mce: Add __mcsafe_copy()

[Andy Lutomirski]

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