linux-kernel - Re: [PATCH 3/4] KVM: x86: introduce get_kvmclock

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Message-ID: <20160902170734.6jcgc3qmaf43jblr@rkaganb.sw.ru>
Date:   Fri, 2 Sep 2016 20:07:34 +0300
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <peterhornyack@...gle.com>, <rkrcmar@...hat.com>, <den@...nvz.org>
Subject: Re: [PATCH 3/4] KVM: x86: introduce get_kvmclock_ns

On Fri, Sep 02, 2016 at 06:57:10PM +0200, Paolo Bonzini wrote:
> 
> 
> On 02/09/2016 18:55, Roman Kagan wrote:
> >> > I'll change patch 4 to store the parameters and use them when accessing
> >> > the time reference counter MSR.  I'll still keep the procedure that goes
> >> > through kvmclock.  It's a bit more involved for the scale, but
> >> > vcpu->last_guest_tsc only provides a part of the offset computation; the
> >> > other half is vcpu->hv_clock.system_time and it's not stored anywhere.
> > Erm... It is stored right there, in vcpu->hv_clock.system_time, you can
> > access it just fine when you populate tsc_ref_page values.  Am I missing
> > anything?
> 
> No.  It's not stored anywhere outside vcpu->hv_clock.  My reasoning goes
> that if I have to use vcpu->hv_clock.system_time I might as well use
> vcpu->hv_clock for everything. :)

Well, there're plenty of ways to bring the necessary values to where
they are needed.

But that's a matter of simplicity, not correctness, so I won't mind that
much.

Thanks,
Roman.