Messages in this thread | | | Date | Wed, 7 Dec 2005 11:01:46 -0500 (EST) | From | Alan Stern <> | Subject | Re: [linux-usb-devel] Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t. |
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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.
Sure, a locked cycle has a certain expense. But it's a lot less than the expense of a contested spinlock. On the other hand, many times UP systems can eliminate spinlocks entirely. There are lots of variables and many possible tradeoffs.
Alan Stern
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