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

Roman Zippel
2005-01-14T03:39:16Z

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.

bye, Roman