On Thu, Jan 02, 2014 at 05:08:07PM +0100, Peter Lieven wrote:
> > Not using irq disable/enable pairs. The subtraction is not dependant on
> > any particular time.
> >
> > local_irq_disable();
> > now_ns = get_kernel_ns();
> > local_irq_enable();
> > delta = user_ns.clock - now_ns;
> >
> > Any interrupt that would affect the value of get_kernel_ns(), would
> > have a similar effect before the interrupts are disabled. So the
> > disable/enable pair achieves nothing in practice. It was copied from
> > kvm_guest_time_update.
> >
> >
>
> Thanks for clarifying. What about get_kernel_ns() can't this be interrupted?
>
> Peter
It can handle interrupts.
Disabling interrupts there is used when a
{rdtsc, system_time=get_kernel_ns()} tuple is wanted, to reduce
the physical time difference between execution of rdtsc and get_kernel_ns().
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