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rcu: Elevate priority of offloaded callback threads

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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: Alison Chaiken <achaiken@aurora.tech>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Alison Chaiken 2022-01-11 15:32:52 -08:00 committed by Paul E. McKenney
parent 54577e23fa
commit c8b16a6526
2 changed files with 4 additions and 1 deletions
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2
kernel/rcu/tree.c
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@ -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);

3
kernel/rcu/tree_nocb.h
View file

@ -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);
}