On Thu, Apr 13, 2017 at 10:31:00AM -0700, Paul E. McKenney wrote: > On Thu, Apr 13, 2017 at 07:04:34PM +0200, Peter Zijlstra wrote: > > On Thu, Apr 13, 2017 at 09:55:16AM -0700, Paul E. McKenney wrote: > > > > > To avoid people tuning huge machines having to wait for me to give > > > > > them an answer as to why they are suffering lock contention after > > > > > cranking up the value of RCU_FANOUT_LEAF. > > > > So is there a good reason to increase FANOUT_LEAF ? > > Increasing it reduces the number of rcu_node structures, and thus the > number of cache misses during grace-period initialization and cleanup. > This has proven necessary in the past on large machines having long > memory latencies. And there are starting to be some pretty big machines > running in production, and even for typical commerical workloads.
Is that perhaps a good moment to look at aligning the cpus in said nodes with the cache topology?