On Thursday 01 February 2007 15:29, Jiri Bohac wrote:
> If I do:
> rdtscll(a)
> ...
> rdtscll(b)
> is it guaranteed that (b > a) ?
It's not architecturally -- unless you have a barrier.
On P4 the micro architecture guarantees it, but there the barrier in
get_cycles_sync is patched away. On other x86-64s it is generally needed.
The effect can be also seen between CPUs.
> Because of the __vxtime.cpu[cpu].tsc_invalid flag. We may be
You can still precompute it for the HPET etc. case.
They are already slow, but saving a condition there might be still
worth it.
-Andi
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