linux-kernel - Re: [PATCH v3 4/6] KVM-GST: KVM Steal time registration

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Date:	Tue, 15 Feb 2011 16:48:47 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH v3 4/6] KVM-GST: KVM Steal time registration

On Tue, 2011-02-15 at 16:41 +0200, Avi Kivity wrote:
> > +static int kvm_register_steal_time(void)
> > +{
> > +     int cpu = smp_processor_id();
> > +     int low, high, ret;
> > +     struct kvm_steal_time *st =&per_cpu(steal_time, cpu);
> > +
> > +     if (!hypervisor_steal_time)
> > +             return 0;
> 
> You're using hypervisor_steal_time to communicate the existence of the 
> feature.  Yuck. 

Yeah, ideally we make steal_time_clock() a proper paravirt op with:

u64 native_steal_time_clock(int cpu)
{
	WARN_ONCE(1, "Using steal_time_clock() on actual hardware..\n");
	return 0;
}

And use paravirt_enabled() to avoid calling it where possible. Then once
we have all the jump_label stuff sorted we can make paravirt_enabled() a
static_branch() and it'll just go away on native.


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