Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

H. Peter Anvin
2012-06-12T20:58:48Z

On 06/12/2012 01:56 PM, Borislav Petkov wrote:
> On Tue, Jun 12, 2012 at 01:42:07PM -0700, H. Peter Anvin wrote:
>> I personally don't know of any valid use case for per-core loads, and
>> it sounds like a horrid idea.
>
> Vehemently agreed.
>
> However, last time we talked about Ingo mentioned some possibility
> of having different microcode versions on different CPUs:
> http://lkml.indiana.edu/hypermail/linux/kernel/1105.3/00749.html
>
> Hmm...
>
>> And yes, I would prefer a single sysfs file, or better yet a plain old
>> device node.
>
> Also agreed.
>

There is a difference here. Mixed steppings or even mixed CPUs are,
indeed, supported (even things like Nehalem + Westmere in the same
system). However, the notion is that we should upload the *entire set*
of microcodes to the kernel, and let it flash the appropriate one into
each CPU.

This may result in different version number on different CPUs.

-hpa