From c0f489d2c6fec8994c642c2ec925eb858727dc7b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 4 Jun 2014 13:46:03 -0700 Subject: rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs Binding the grace-period kthreads to the timekeeping CPU resulted in significant performance decreases for some workloads. For more detail, see: https://lkml.org/lkml/2014/6/3/395 for benchmark numbers https://lkml.org/lkml/2014/6/4/218 for CPU statistics It turns out that it is necessary to bind the grace-period kthreads to the timekeeping CPU only when all but CPU 0 is a nohz_full CPU on the one hand or if CONFIG_NO_HZ_FULL_SYSIDLE=y on the other. In other cases, it suffices to bind the grace-period kthreads to the set of non-nohz_full CPUs. This commit therefore creates a tick_nohz_not_full_mask that is the complement of tick_nohz_full_mask, and then binds the grace-period kthread to the set of CPUs indicated by this new mask, which covers the CONFIG_NO_HZ_FULL_SYSIDLE=n case. The CONFIG_NO_HZ_FULL_SYSIDLE=y case still binds the grace-period kthreads to the timekeeping CPU. This commit also includes the tick_nohz_full_enabled() check suggested by Frederic Weisbecker. Reported-by: Jet Chen Signed-off-by: Paul E. McKenney [ paulmck: Created housekeeping_affine() and housekeeping_mask per fweisbec feedback. ] --- include/linux/tick.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'include/linux/tick.h') diff --git a/include/linux/tick.h b/include/linux/tick.h index b84773cb9f4c..06cc093ab7ad 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -12,6 +12,7 @@ #include #include #include +#include #ifdef CONFIG_GENERIC_CLOCKEVENTS @@ -162,6 +163,7 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } #ifdef CONFIG_NO_HZ_FULL extern bool tick_nohz_full_running; extern cpumask_var_t tick_nohz_full_mask; +extern cpumask_var_t housekeeping_mask; static inline bool tick_nohz_full_enabled(void) { @@ -194,6 +196,24 @@ static inline void tick_nohz_full_kick_all(void) { } static inline void __tick_nohz_task_switch(struct task_struct *tsk) { } #endif +static inline bool is_housekeeping_cpu(int cpu) +{ +#ifdef CONFIG_NO_HZ_FULL + if (tick_nohz_full_enabled()) + return cpumask_test_cpu(cpu, housekeeping_mask); +#endif + return true; +} + +static inline void housekeeping_affine(struct task_struct *t) +{ +#ifdef CONFIG_NO_HZ_FULL + if (tick_nohz_full_enabled()) + set_cpus_allowed_ptr(t, housekeeping_mask); + +#endif +} + static inline void tick_nohz_full_check(void) { if (tick_nohz_full_enabled()) -- cgit v1.2.3