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

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Message-ID: <20170227140500.GX6500@twins.programming.kicks-ass.net>
Date:   Mon, 27 Feb 2017 15:05:00 +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 09:48:35PM +0800, Wanpeng Li wrote:
> 2017-02-27 20:43 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> > I have no clue what that tries to do.
> 
> The patch tries to mark sched clock stable if
> KVM_FEATURE_CLOCKSOURCE_STABLE_BIT / PVCLOCK_TSC_STABLE_BIT is set in
> kvm guest even if there is no invariant tsc cpuid bit.

I just ripped out the interface to 'set stable' for good reasons. Also,
the branch you add it to doesn't in fact do clear_stable -- so who does?

Also, the sched/clock.c code shouldn't know about hypervisor anything.

So whatever it is you're doing, you're doing it wrong.