[Xen-devel] Re: Linux questions

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 4/12/07 11:13, "Andi Kleen" <andi@xxxxxxxxxxxxxx> wrote:

>>> I have to disagree: At least the uses of barrier() in monotonic_clock()
>>> appear
>>> to be in places where in reality (and from a theoretical standpoint) rmb()
>>> ought to be used.
>> 
>> We're sync'ing against concurrent updates of a this_cpu variable. We can
>> only race updates in a local ISR, and hence barrier() suffices.
> 
> Not if you use RDTSC inside the loop.

I must disagree! And I *know* that RDTSC is not a serialising instruction...

If we race, then there was an interrupt. Interrupt delivery is a
serialisation point for the interrupted instruction stream.

 -- Keir



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