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

H. Peter Anvin
2012-06-12T20:42:29Z

On 06/12/2012 01:37 PM, Borislav Petkov wrote:
> On Tue, Jun 12, 2012 at 01:28:55PM -0700, H. Peter Anvin wrote:
>> On 06/12/2012 12:49 PM, Borislav Petkov wrote:
>>>
>>> Also, I'd assume we need some of the current functionality to be able to
>>> load ucode without rebooting the box.
>>>
>>
>> Yes, the basic idea is that we'll keep the ucode around anyway so we can
>> feed it to hotplug CPUs or S3 resume. If the ucode is updated from
>> userspace we'd replace the in-memory copy and load it into the CPUs.
>
> You say CPUs, i.e. plural. What is your take on loading ucode on a
> single core, i.e. the /sys/devices/system/cpu/cpuX/microcode/reload
> interface? Do you guys need to load ucode only system-wide or can you
> stomach per-core loads?
>
> I want to disable it (or even remove it, modulo the whole userspace
> compat blah blah) on AMD.
>
> Also, if we do system-wide, can we have a single sysfs node where we
> give the new ucode from userspace instead of per-cpu files?
>

I personally don't know of any valid use case for per-core loads, and it
sounds like a horrid idea. And yes, I would prefer a single sysfs file,
or better yet a plain old device node.

-hpa