Re: REGRESSION: Performance regressions from switchinganon_vma->lock to mutex

[Andi Kleen]

> On 2.6.39, the contention of anon_vma->lock occupies 3.25% of cpu.
> However, after the switch of the lock to mutex on 3.0-rc2, the mutex
> acquisition jumps to 18.6% of cpu.  This seems to be the main cause of
> the 52% throughput regression.
> 
This patch makes the mutex in Tim's workload take a bit less CPU time
(4% down) but it doesn't really fix the regression. When spinning for a 
value it's always better to read it first before attempting to write it.
This saves expensive operations on the interconnect.

So it's not really a fix for this, but may be a slight improvement for 
other workloads.

-Andi