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Commit 02482880 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make RCU_FANOUT_LEAF help text more explicit about skew_tick 



If you set RCU_FANOUT_LEAF too high, you can get lock contention
on the leaf rcu_node, and you should boot with the skew_tick kernel
parameter set in order to avoid this lock contention.  This commit
therefore upgrades the RCU_FANOUT_LEAF help text to explicitly state
this.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 468d01be

init/Kconfig

+8 −2
Original line number Diff line number Diff line
@@ -612,11 +612,17 @@ config RCU_FANOUT_LEAF 
	  initialization.  These systems tend to run CPU-bound, and thus

	  are not helped by synchronized interrupts, and thus tend to

	  skew them, which reduces lock contention enough that large

	  leaf-level fanouts work well.

	  leaf-level fanouts work well.  That said, setting leaf-level

	  fanout to a large number will likely cause problematic

	  lock contention on the leaf-level rcu_node structures unless

	  you boot with the skew_tick kernel parameter.



	  Select a specific number if testing RCU itself.



	  Select the maximum permissible value for large systems.

	  Select the maximum permissible value for large systems, but

	  please understand that you may also need to set the skew_tick

	  kernel boot parameter to avoid contention on the rcu_node

	  structure's locks.



	  Take the default if unsure.