Re: [PATCH] x86: print microcode revision on PEBs errors

[Ingo Molnar <mingo@kernel.org>]

* Michael S. Tsirkin <mst@redhat.com> wrote:

> On Sandy bridge CPUs with old microcode, PEBs
> fails and suggests a microcode update.
> Print out the required and the actual revision to
> make it easier to figure out what's wrong.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index f31a165..81f2789 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -2105,6 +2105,8 @@ static int intel_snb_pebs_broken(int cpu)
>  		}
>  	}
>  
> +	pr_info("PEBS checking: microcode 0x%x min legal 0x%x\n",
> +		cpu_data(cpu).microcode, rev);

That's not a very informative message though.

Something like:

   "x86/perf/intel: PEBS turned off due to too old microcode version 0x%x\n"
   "x86/perf/intel: Minimum required microcode version for PEBS: 0x%x\n"

would work better I think.

Also, only output this once, and only output it if the check 
_fails_.

>  	return (cpu_data(cpu).microcode < rev);

Btw., please also fix the return statement, it doesn't need 
parentheses.

Thanks,

	Ingo