Re: [PATCH 1/2] percpu-rw-semaphores: use light/heavy barriers

[Peter Zijlstra]

On Tue, 2012-10-23 at 21:23 +0200, Oleg Nesterov wrote:
> I have to admit, I have
> no idea how much cli/sti is slower compared to preempt_disable/enable.
> 
A lot.. esp on stupid hardware (insert pentium-4 reference), but I think
its more expensive for pretty much all hardware, preempt_disable() is
only a non-atomic cpu local increment and a compiler barrier, enable the
same and a single conditional.
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