Re: rcu: performance regression

[Peter Zijlstra]

On Tue, 2011-06-14 at 06:02 -0700, Paul E. McKenney wrote:
> > This commit also cause hackbench process mode performance dropping, and
> > Shaohua's patch do recovered this. But in hackbench testing, the vmstat
> > show context switch have some reduce. And perf tool show
> > root_domain->cpupri->prio_to_cpu[]->lock has contention with the commit.
> 
> Steven, Peter, would any of the recent fixes address this lock contention? 

No. People occasionally run into that thing, but given the constraints
on SCHED_FIFO SMP (run the n highest priority tasks on m cpus; n<=m)
there isn't really much we can do.

IIRC Chris Mason once proposed a lockless version, but that opened up
race windows, Steve might know the details better.
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