Re: [PATCH 1/10] Cr4 is valid on some 486s

[Arjan van de Ven]

> 
> Runtime tricks that increase complexity cost, yes.  It's all a question 
> of measured gain vs. complexity.  But a couple of percent gained on an 
> overall basis can be magnified enormously if you are looking at a 
> workload that stresses a particular path. 

a couple of percents sounds really really high to me. If it's really
that then I think Andi's conclusion is wrong with respect to that
locking cliff; if we spend a few percent of our performance on locks in
the uncontended case we're way over the edge in my opinion.

>  I would expect some of those 
> gains to be non-trivial, especially if considering the optimizations you 
> could do on page table updates knowing you needn't worry about SMP 

page table updates happen in the hypervisor in a xen like
paravirtualized setup right? so that happens outside the kernel..


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