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

Peter Zijlstra
2012-06-15T12:42:58Z

On Fri, 2012-06-15 at 14:37 +0200, Borislav Petkov wrote:
> This is a minimal fix which we'd like to see in stable too thus the
> more-or-less arbitrary decision to allow system-wide reloading only on
> the BSP:
>
> $ echo 1 > /sys/devices/system/cpu/cpu0/microcode/reload
> ...
>
> and disable the interface on the other cores:
>
> $ echo 1 > /sys/devices/system/cpu/cpu23/microcode/reload
> -bash: echo: write error: Invalid argument

One could allow the reload from all cpus and simply do all cpus, but I
guess the rationale for not doing that and restricting it to cpu0 is to
avoid the O(n^2) thing in case userspace issues a reload on all cpus?

If so it would be good to mention in the Changelog so people see its not
a 'random' choice.