Messages in this thread | | | Subject | Re: [linux-usb-devel] Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t. | From | Arjan van de Ven <> | Date | Wed, 07 Dec 2005 17:04:16 +0100 |
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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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