Commit c8b16a65 authored by Alison Chaiken's avatar Alison Chaiken Committed by Paul E. McKenney
Browse files

rcu: Elevate priority of offloaded callback threads 



When CONFIG_PREEMPT_RT=y, the rcutree.kthread_prio command-line
parameter signals initialization code to boost the priority of rcuc
callbacks to the designated value.  With the additional
CONFIG_RCU_NOCB_CPU=y configuration and an additional rcu_nocbs
command-line parameter, the callbacks on the listed cores are
offloaded to new rcuop kthreads that are not pinned to the cores whose
post-grace-period work is performed.  While the rcuop kthreads perform
the same function as the rcuc kthreads they offload, the kthread_prio
parameter only boosts the priority of the rcuc kthreads.  Fix this
inconsistency by elevating rcuop kthreads to the same priority as the rcuc
kthreads.

Signed-off-by: default avatarAlison Chaiken <achaiken@aurora.tech>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 54577e23

kernel/rcu/tree.c

+1 −1
Original line number Diff line number Diff line
@@ -153,7 +153,7 @@ static void sync_sched_exp_online_cleanup(int cpu); 
static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);

static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);



/* rcuc/rcub kthread realtime priority */

/* rcuc/rcub/rcuop kthread realtime priority */

static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;

module_param(kthread_prio, int, 0444);

kernel/rcu/tree_nocb.h

+3 −0
Original line number Diff line number Diff line
@@ -1270,6 +1270,9 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) 
			"rcuo%c/%d", rcu_state.abbr, cpu);

	if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))

		return;



	if (kthread_prio)

		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

	WRITE_ONCE(rdp->nocb_cb_kthread, t);

	WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);

}