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SubjectRe: [git pull] scheduler updates
On Sat, 8 Nov 2008 10:28:21 -0800 (PST)
Linus Torvalds <torvalds@linux-foundation.org> wrote:

>
>
> On Sat, 8 Nov 2008, Ingo Molnar wrote:
> >
> > Ingo Molnar (2):
> > sched: improve sched_clock() performance
> > sched: optimize sched_clock() a bit
>
> Btw, why do we do that _idiotic_ rdtsc_barrier() AT ALL?
>
> No sane user can possibly want it. If you do 'rdtsc', there's nothing
> you can do about a few cycles difference due to OoO _anyway_. Adding
> barriers is entirely meaningless - it's not going to make the return
> value mean anything else.
>
> Can we please just remove that idiocy? Or can somebody give a _sane_
> argument for it?

historically it was for early AMD cpus (K7, not sure if early K8 did
this) where 2 consecutive rdtsc's in the same codestream would get
reordered compared to eachother, so you could observe the tsc go
backwards...



--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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