Re: [Xen-devel] RT Xen on ARM - R-Car series

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

On 15.02.19 19:13, Julien Grall wrote:
> Not really... This is an implementation details that does not matter
> on the OS side.
And on hypervisor side?

> If you want accurate number, then the NOW() macro is not sufficient
> enough. Read to CNTPCTL_EL0 can occur speculatively and out of order
> relative to other instructions executed on the same PE. So the PE can
> potentially execute CNTPCTL_EL0 before update_runstate_area(...).
>
> You would want to add an isb() at least before NOW() and potentially
> after (unless you have register dependency).
> I have a patch for adding an isb()  in the NOW() macro. I will send it later 
> on.Good hint.
> >            update_runstate_area(current);
> >
> > +        if (current->domain->domain_id == 1)
> > +            printk("cp = %"PRI_stime"\n", NOW()-t);
> That's only one number.  Did you do an average over multiple context
> switch (say 1000) ?
No, just got them on the console to see the numbers. They seems to not change 
significantly during a minute run.
That's why I did not answer about context switches number.

I can do it in a bit more complicated way. But I do not expect I would 
encounter differences.

--
Sincerely,
Andrii Anisov.

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