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

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Message-ID: <20160902152439.xraq7pmtryd2nkta@rkaganb.sw.ru>
Date:   Fri, 2 Sep 2016 18:24:40 +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 Thu, Sep 01, 2016 at 05:26:14PM +0200, Paolo Bonzini wrote:
> Introduce a function that reads the exact nanoseconds value that is
> provided to the guest in kvmclock.  This crystallizes the notion of
> kvmclock as a thin veneer over a stable TSC, that the guest will
> (hopefully) convert with NTP.  In other words, kvmclock is *not* a
> paravirtualized host-to-guest NTP.

It might also be worth documenting this approach in a comment somewhere
around pvclock_gtod_notify / update_pvclock_gtod or friends.  And, if
those could be simplified due to this change, it would be great, too.

Roman.