rcu: Move RCU grace-period initialization into a kthread

As the first step towards allowing grace-period initialization to be
preemptible, this commit moves the RCU grace-period initialization
into its own kthread.  This is needed to keep large-system scheduling
latency at reasonable levels.

Also change raw_spin_lock_irqsave() to raw_spin_lock_irq() as suggested
by Peter Zijlstra in review comments.

Reported-by: Mike Galbraith <mgalbraith@suse.de>
Reported-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 4d29169f2124..117a15019e99 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -385,6 +385,9 @@ struct rcu_state {
         u8      boost;                          /* Subject to priority boost. */
         unsigned long gpnum;                    /* Current gp number. */
         unsigned long completed;                /* # of last completed gp. */
+        struct task_struct *gp_kthread;         /* Task for grace periods. */
+        wait_queue_head_t gp_wq;                /* Where GP task waits. */
+        int gp_flags;                           /* Commands for GP task. */
 
         /* End of fields guarded by root rcu_node's lock. */