RE: [Xen-devel] [RFC] Correct/fast timestamping in apps under Xen [0 of 4]

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> I think you're missing a couple of premises here:
>
>0) It is not possible to update the existing APIs and 
> ABIs available to applications to meet the most demanding
> performance requirements.

I think this was covered nicely in the first paragraph
where I said "in a wide range of hardware and software
conditions."

>5) There will be enough important applications (ie, broadly used,
> rather than a few in-house apps) whose developers are willing to
> update them to your new proposed ABI to justify adding and
> maintaining these new ABIs.

I guess you'll have to trust me on that one (sez
Dan at ORACLE.com) ;-)

Jeremy, I've heard that people are tiring of reading all
of our public jousting around this topic (though I've found
it useful in many ways), and I'm trying to make forward
progress here, so I'd prefer to hear from other
reviewers or at least I'd appreciate more constructive
feedback.

Thanks,
Dan

> -----Original Message-----
> From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx]
> Sent: Friday, October 02, 2009 1:00 PM
> To: Dan Magenheimer
> Cc: Xen-Devel (E-mail); Kurt Hackel; Ian Pratt; Keir Fraser
> Subject: Re: [Xen-devel] [RFC] Correct/fast timestamping in apps under
> Xen [0 of 4]
> 
> 
> On 10/02/09 10:50, Dan Magenheimer wrote:
> > The premises are:
> >
> > 1) A large and growing percentage of servers running
> >    Xen have a "reliable" TSC and Xen can determine
> >    conclusively whether a server does or does not
> >    have a reliable TSC.
> > 2) A small but growing percentage of servers running
> >    Xen implement the rdtscp instruction but Xen does
> >    not and will not expose this instruction to guest
> >    OSes.
> > 3) Xen is able to track the "incarnation" number for
> >    a guest.  This number will increase whenever a
> >    guest is restored or migrated (and possibly more
> >    frequently).  Optionally, an administrator can
> >    explicitly mark a guest as "landlocked", disallowing
> >    save/restore/migration for that guest.
> > 4) Apps can become "virtualization aware" in that
> >    they can access certain information directly
> >    from Xen utilizing an OS-independent mechanism.
> >    This information includes not only "Am I running
> >    on Xen?" but also, for example, "Is TSC reliable
> >    on this physical machine?", "Is rdtsc emulated
> >    or native on this virtual machine?",  "What is
> >    the current incarnation number for this virtual
> >    machine?", "Is this virtual machine landlocked?",
> >    "What are the pvclock parameters for this
> >    virtual machine?", etc.
> >   
> 
> I think you're missing a couple of premises here:
> 
>     0) It is not possible to update the existing APIs and 
> ABIs available
>     to applications to meet the most demanding performance 
> requirements.
> 
>     5) There will be enough important applications (ie, broadly used,
>     rather than a few in-house apps) whose developers are willing to
>     update them to your new proposed ABI to justify adding and
>     maintaining these new ABIs.
> 
> Without discussing these, you're presupposing your solution 
> is necessary.
> 
>     J
> 
>

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