Re: page table lock patch V15 [0/7]: overview

[Andi Kleen]

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.

-Andi
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