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

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Message-ID: <20170227124349.GU6515@twins.programming.kicks-ass.net>
Date:   Mon, 27 Feb 2017 13:43:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: tip.today - scheduler bam boom crash (cpu hotplug)

On Mon, Feb 27, 2017 at 08:30:11PM +0800, Wanpeng Li wrote:

> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index 2a5cafd..542710b 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -107,12 +107,12 @@ static inline void kvm_sched_clock_init(bool stable)
> >  {
> >         if (!stable) {
> >                 pv_time_ops.sched_clock = kvm_clock_read;
> > +               clear_sched_clock_stable();
> >                 return;
> >         }
> >
> >         kvm_sched_clock_offset = kvm_clock_read();
> >         pv_time_ops.sched_clock = kvm_sched_clock_read;
> > -       set_sched_clock_stable();
> 
> This results in sched clock always unstable for kvm guest since there
> is no invariant tsc cpuid bit exposed for kvm guest currently. 

What the heck is KVM_FEATURE_CLOCKSOURCE_STABLE_BIT /
PVCLOCK_TSC_STABLE_BIT about then?

> How about something like below(untested):

I have no clue what that tries to do.