RE: [Xen-ia64-devel] Question about migration

[Alex Williamson <alex.williamson@xxxxxx>]

On Sat, 2008-02-02 at 09:43 +0800, Xu, Anthony wrote:
> Kouya Shimura wrote:
> > Hi,
> > 
> > In a SMP machine, complete synchronizing ITCs is impossible.
> Agree,
> 
> But the difference is limited in a small range,
> So, when application is migrated to another CPU, it will see ITC > what
> it saw last time.
> That means, itc difference have to be less than the itc cycle spent on
> process switch.
> Otherwise, linux kernel needs to re sync the ITC.

  The kernel guarantees applications only see time move forward, even
across multiple CPUs.  See:

kernel/timer.c:time_interpolator_get_counter()

We never return a time before last_cycle unless booted with the
"nojitter" options.

        Alex

-- 
Alex Williamson                             HP Open Source & Linux Org.


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