Re: [Xen-devel] [PATCH] xen: add steal_clock support on x86

Dario Faggioli
2016-05-19T03:36:31Z

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On Wed, 2016-05-18 at 12:03 -0600, Tony S wrote:
> On Wed, May 18, 2016 at 11:59 AM, Tony S <suokunstar@gmail.com>
> wrote:
> > On Wed, May 18, 2016 at 11:20 AM, Boris Ostrovsky
> > <boris.ostrovsky@oracle.com> wrote:
> > > Tony narrowed the problem down to update_curr() where vruntime is
> > > calculated, based on runqueue's clock_task value. That value is
> > > computed
> > > in update_rq_clock_task(), which needs paravirt_steal_rq_enabled.
> > >
> > Hi Boris,
> >
> > You are right.
> >
> > The real problem is steal_clock in pv_time_ops is implemented in
> > KVM
> > but not in Xen.
> >
> > [...]
> >
> > Therefore, even though update_rq_clock_task() calculates the value
> > and
> > paravirt_steal_rq_enabled option is enabled, the steal value just
> > returns 0. This will cause the problem which I mentioned.
> >
> > update_rq_clock_task
> > --> paravirt_steal_clock
> > --> pv_time_ops.steal_clock
> > --> native_steal_clock (if in Xen)
> > --> 0
> >
Ok, thanks again for confirming this.

> Also, I tried the latest long term version of Linux 4.4, this issue
> still exists there. Hoping the next version can add this patch.
>
Yes, as Juergen said here:

http://lists.xen.org/archives/html/xen-devel/2016-05/msg01712.html

he has in his plans to implement the full mechanism. It will just take
a bit longer, due to the amount of work necessary for this second part.

Regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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