From: Frederic Weisbecker frederic@kernel.org
commit f268c3737ecaefcfeecfb4cb5e44958a8976f067 upstream.
Checking for and processing RCU-nocb deferred wakeup upon user/guest entry is only relevant when nohz_full runs on the local CPU, otherwise the periodic tick should take care of it.
Make sure we don't needlessly pollute these fast-paths as a -3% performance regression on a will-it-scale.per_process_ops has been reported so far.
Fixes: 47b8ff194c1f (entry: Explicitly flush pending rcuog wakeup before last rescheduling point) Fixes: 4ae7dc97f726 (entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point) Reported-by: kernel test robot oliver.sang@intel.com Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Paul E. McKenney paulmck@kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210527113441.465489-1-frederic@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/entry-kvm.h | 3 ++- include/linux/tick.h | 7 +++++++ kernel/entry/common.c | 5 +++-- kernel/time/tick-sched.c | 1 + 4 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h index 8b2b1d68b954..136b8d97d8c0 100644 --- a/include/linux/entry-kvm.h +++ b/include/linux/entry-kvm.h @@ -3,6 +3,7 @@ #define __LINUX_ENTRYKVM_H
#include <linux/entry-common.h> +#include <linux/tick.h>
/* Transfer to guest mode work */ #ifdef CONFIG_KVM_XFER_TO_GUEST_WORK @@ -57,7 +58,7 @@ int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu); static inline void xfer_to_guest_mode_prepare(void) { lockdep_assert_irqs_disabled(); - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare(); }
/** diff --git a/include/linux/tick.h b/include/linux/tick.h index 7340613c7eff..1a0ff88fa107 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -11,6 +11,7 @@ #include <linux/context_tracking_state.h> #include <linux/cpumask.h> #include <linux/sched.h> +#include <linux/rcupdate.h>
#ifdef CONFIG_GENERIC_CLOCKEVENTS extern void __init tick_init(void); @@ -300,4 +301,10 @@ static inline void tick_nohz_task_switch(void) __tick_nohz_task_switch(); }
+static inline void tick_nohz_user_enter_prepare(void) +{ + if (tick_nohz_full_cpu(smp_processor_id())) + rcu_nocb_flush_deferred_wakeup(); +} + #endif diff --git a/kernel/entry/common.c b/kernel/entry/common.c index a0b3b04fb596..bf16395b9e13 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -5,6 +5,7 @@ #include <linux/highmem.h> #include <linux/livepatch.h> #include <linux/audit.h> +#include <linux/tick.h>
#include "common.h"
@@ -186,7 +187,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, local_irq_disable_exit_to_user();
/* Check if any of the above work has queued a deferred wakeup */ - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare();
ti_work = READ_ONCE(current_thread_info()->flags); } @@ -202,7 +203,7 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs) lockdep_assert_irqs_disabled();
/* Flush pending rcuog wakeup before the last need_resched() check */ - rcu_nocb_flush_deferred_wakeup(); + tick_nohz_user_enter_prepare();
if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 828b091501ca..6784f27a3099 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -230,6 +230,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
#ifdef CONFIG_NO_HZ_FULL cpumask_var_t tick_nohz_full_mask; +EXPORT_SYMBOL_GPL(tick_nohz_full_mask); bool tick_nohz_full_running; EXPORT_SYMBOL_GPL(tick_nohz_full_running); static atomic_t tick_dep_mask;