linux-kernel - Re: [PATCH 1/1] perf/x86: Use KERN_INFO when checking PMU fails on virtual environment

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Date:	Mon, 29 Sep 2014 23:19:23 -0500
From:	Wei Huang <wei@...hat.com>
To:	linux-kernel@...r.kernel.org
CC:	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH 1/1] perf/x86: Use KERN_INFO when checking PMU fails on
 virtual environment

Hi Ingo, tglx and hpa,

Any comment on this patch? Thanks.

-Wei

On 09/24/2014 10:55 PM, Wei Huang wrote:
> PMU checking can fail due to various reasons. On native machine,
> this is mostly caused by faulty hardware and it is reasonable to
> use KERN_ERR in reporting. However, when kernel is running on
> virtualized environment, this checking can fail if virtual PMU is
> not supported (e.g. KVM on AMD host). It is annoying to see
> an error message on splash screen, even though we know such failure
> is benign on virtualized environment.
>
> This patch checks if kernel is running in virtualized environment.
> If so, it will use KERN_INFO in reporting. This patch was tested
> successfully on KVM.
>
> Signed-off-by: Wei Huang <wei@...hat.com>
> ---
>   arch/x86/kernel/cpu/perf_event.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 918d75f..16c7302 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -243,7 +243,8 @@ static bool check_hw_exists(void)
>
>   msr_fail:
>   	printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");
> -	printk(KERN_ERR "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
> +	printk(boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_INFO : KERN_ERR
> +	       "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
>
>   	return false;
>   }
>
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