linux-kernel - Re: [RFC 0/2] kvm: Use host timekeeping in guest.

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Date:   Tue, 24 Sep 2019 17:08:53 +0900
From:   Suleiman Souhlal <suleiman@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        john.stultz@...aro.org, sboyd@...nel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        kvm@...r.kernel.org, Tomasz Figa <tfiga@...gle.com>
Subject: Re: [RFC 0/2] kvm: Use host timekeeping in guest.

On Fri, Sep 20, 2019 at 7:23 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Fri, 20 Sep 2019, Paolo Bonzini wrote:
>
> > On 20/09/19 08:27, Suleiman Souhlal wrote:
> > > To do that, I am changing kvmclock to request to the host to copy
> > > its timekeeping parameters (mult, base, cycle_last, etc), so that
> > > the guest timekeeper can use the same values, so that time can
> > > be synchronized between the guest and the host.
> > >
> > > Any suggestions or feedback would be highly appreciated.
> >
> > I'm not a timekeeping maintainer, but I don't think the
> > kernel/time/timekeeping.c changes are acceptable.
>
> Indeed. #ifdef WHATEVERTHEHECK does not go anywhere. If at all this needs
> to be a runtime switch, but I have yet to understand the whole picture of
> this.

Yeah, I will try to make this a runtime switch.

As for the PTP driver, I don't think it will work for us because we
need CLOCK_MONOTONIC and CLOCK_BOOTTIME to match the host, and from my
understanding, PTP doesn't solve that.

Thanks,
-- Suleiman