linux-kernel - Re: tip.today - scheduler bam boom crash (cpu hotplug)

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Date:   Mon, 27 Feb 2017 18:40:46 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: tip.today - scheduler bam boom crash (cpu hotplug)

On Mon, 27 Feb 2017, Paolo Bonzini wrote:
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 2724dc82f992..3080b6877190 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -1398,6 +1398,9 @@ void __init tsc_init(void)
> 
>  	use_tsc_delay();
> 
> +	if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
> +		mark_tsc_unstable("not invariant");

Errm, no. 

That makes TSC unusable for systems which do not go into C/P states in
which the TSC stops. There is a world outside KVM ....

Thanks,

	tglx