[Xen-devel] Re: Linux questions

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 4/12/07 11:44, "Andi Kleen" <andi@xxxxxxxxxxxxxx> wrote:

>> 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.
> 
> The synchronization relies on the RDTSC happening between the
> two sequence number checks. Otherwise you can get inconsistent state
> between RDTSC and the xtime data which might be changing asynchronously
> on another CPU. Therefore you need RDTSC barriers.

Our monotonic_clock() implementation does not reference xtime nor its
seqlock. If it did, you would be correct.

 -- Keir



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