Messages in this thread | | | Date | 14 Jan 2005 05:14:21 +0100 | Date | Fri, 14 Jan 2005 05:14:21 +0100 | From | Andi Kleen <> | Subject | Re: page table lock patch V15 [0/7]: overview |
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On Fri, Jan 14, 2005 at 04:39:16AM +0100, Roman Zippel wrote: > Hi, > > Christoph Lameter wrote: > > >Introduction of the cmpxchg is one atomic operations that replaces the two > >spinlock ops typically necessary in an unpatched kernel. Obtaining the > >spinlock requires an spinlock (which is an atomic operation) and then the > >release involves a barrier. So there is a net win for all SMP cases as far > >as I can see. > > But there might be a loss in the UP case. Spinlocks are optimized away, > but your cmpxchg emulation enables/disables interrupts with every access.
Only for 386s and STI/CLI is quite cheap there.
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