For kernel built with PREEMPT_RCU=y and RCU_STRICT_GRACE_PERIOD=y, currently, the irq-work will be triggered by high frequency to make the scheduler re-evaluate and call hooks to check whether there are qs need to report when exit RCU read critical section in irq-disbaled context. however if there is no gp in progress, the irq-work trigger is meaningless. This commit reduced irq-work trigger frequency by check whether the current CPU is not experiencing qs or there is task that blocks the current grace period for RCU_STRICT_GRACE_PERIOD=y kernel. The test results are as follows: echo rcu_preempt_deferred_qs_handler > /sys/kernel/debug/tracing/set_ftrace_filter echo 1 > /sys/kernel/debug/tracing/function_profile_enabled insmod rcutorture.ko sleep 20 rmmod rcutorture.ko echo 0 > /sys/kernel/debug/tracing/function_profile_enabled echo > /sys/kernel/debug/tracing/set_ftrace_filter head /sys/kernel/debug/tracing/trace_stat/function* original: ==> /sys/kernel/debug/tracing/trace_stat/function0 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 838746 182650.3 us 0.217 us 0.004 us ==> /sys/kernel/debug/tracing/trace_stat/function1 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 841768 191138.6 us 0.227 us 0.024 us ==> /sys/kernel/debug/tracing/trace_stat/function2 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 828243 180455.6 us 0.217 us 0.004 us ==> /sys/kernel/debug/tracing/trace_stat/function3 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 810258 189158.1 us 0.233 us 0.023 us apply patch: ==> /sys/kernel/debug/tracing/trace_stat/function0 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 302373 67434.95 us 0.223 us 0.001 us ==> /sys/kernel/debug/tracing/trace_stat/function1 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 307174 68398.34 us 0.222 us 0.002 us ==> /sys/kernel/debug/tracing/trace_stat/function2 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 250910 56157.42 us 0.223 us 0.002 us ==> /sys/kernel/debug/tracing/trace_stat/function3 <== Function Hit Time Avg s^2 -------- --- ---- --- --- rcu_preempt_deferred_qs_handle 279902 62644.64 us 0.223 us 0.003 us Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx> --- kernel/rcu/tree_plugin.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index b76076014e12..1514909cf905 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -641,7 +641,8 @@ static void rcu_read_unlock_special(struct task_struct *t) expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) || (rdp->grpmask & READ_ONCE(rnp->expmask)) || - IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) || + (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && + ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) || (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled && t->rcu_blocked_node); // Need to defer quiescent state until everything is enabled. -- 2.25.1
