tree 8f088c805ed43c898543f1e74d21e808605143fc
parent 60cc43fc888428bb2f18f08997432d426a243338
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1517551538 -0800
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1526405144 -0700

rcu: Parallelize expedited grace-period initialization

The latency of RCU expedited grace periods grows with increasing numbers
of CPUs, eventually failing to be all that expedited.  Much of the growth
in latency is in the initialization phase, so this commit uses workqueues
to carry out this initialization concurrently on a rcu_node-by-rcu_node
basis.

This change makes use of a new rcu_par_gp_wq because flushing a work
item from another work item running from the same workqueue can result
in deadlock.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>