On Wed, 2005-12-07 at 11:01 -0500, Alan Stern wrote:
> On Wed, 7 Dec 2005, Arjan van de Ven wrote:
>
> > > On the other hand, Oliver needs to be careful about claiming too much. In
> > > general atomic_t operations _are_ superior to the spinlock approach.
> >
> > No they're not. Both are just about equally expensive cpu wise,
> > sometimes the atomic_t ones are a bit more expensive (like on parisc
> > architecture). But on x86 in either case it's a locked cycle, which is
> > just expensive no matter which side you flip the coin...
>
> You're overgeneralizing.
to some degree yes.
>
> Sure, a locked cycle has a certain expense. But it's a lot less than the
> expense of a contested spinlock.
the chances that *this* spinlock ends up being contested are near zero,
and.. in that scenario a locked cycle does the same thing, just in
hardware..... (eg the other cpu will busy wait until this locked cycle
is done)
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