It was discovered that isolated CPUs could sometimes be disturbed by kworkers processing kfree_rcu() works causing higher than expected latency. It is because the RCU core uses "system_wq" which doesn't have the WQ_UNBOUND flag to handle all its work items. Fix this violation of latency limits by using "system_unbound_wq" in the RCU core instead. This will ensure that those work items will not be run on CPUs marked as isolated. Beside the WQ_UNBOUND flag, the other major difference between system_wq and system_unbound_wq is their max_active count. The system_unbound_wq has a max_active of WQ_MAX_ACTIVE (512) while system_wq's max_active is WQ_DFL_ACTIVE (256) which is half of WQ_MAX_ACTIVE. Reported-by: Vratislav Bendel <vbendel@xxxxxxxxxx> Closes: https://issues.redhat.com/browse/RHEL-50220 Signed-off-by: Waiman Long <longman@xxxxxxxxxx> --- kernel/rcu/tasks.h | 4 ++-- kernel/rcu/tree.c | 8 ++++---- 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e641cc681901..494aa9513d0b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3539,10 +3539,10 @@ schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) if (delayed_work_pending(&krcp->monitor_work)) { delay_left = krcp->monitor_work.timer.expires - jiffies; if (delay < delay_left) - mod_delayed_work(system_wq, &krcp->monitor_work, delay); + mod_delayed_work(system_unbound_wq, &krcp->monitor_work, delay); return; } - queue_delayed_work(system_wq, &krcp->monitor_work, delay); + queue_delayed_work(system_unbound_wq, &krcp->monitor_work, delay); } static void @@ -3634,7 +3634,7 @@ static void kfree_rcu_monitor(struct work_struct *work) // be that the work is in the pending state when // channels have been detached following by each // other. - queue_rcu_work(system_wq, &krwp->rcu_work); + queue_rcu_work(system_unbound_wq, &krwp->rcu_work); } } @@ -3704,7 +3704,7 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && !atomic_xchg(&krcp->work_in_progress, 1)) { if (atomic_read(&krcp->backoff_page_cache_fill)) { - queue_delayed_work(system_wq, + queue_delayed_work(system_unbound_wq, &krcp->page_cache_work, msecs_to_jiffies(rcu_delay_page_cache_fill_msec)); } else { -- 2.43.5
