Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather thanrcu

[Christoph Lameter]

Paul E. McKenney wrote:

>> RCU is problematic because it lets cachelines get cold. A hot cacheline that
>> is used frequently read and written to by the same cpu is very good thing for
>> performace.
> 
> So on your these large boxes, read-only cachelines are preferentially
> ejected from the cache, so that one should write to per-CPU data
> occasionally to keep it resident?  Or is the issue the long RCU grace
> periods which allow the structure being freed to age out of all relevant
> caches?  (My guess would be the second.)

The issue are the RCU grace period that are generally long enough to make the
cacheline fall out of all caches.
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