From: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
When total number of VCPUs of system is less than or equal to physical CPUs,
PLE exits become costly since each VCPU can have dedicated PCPU, and
trying to find a target VCPU to yield_to just burns time in PLE handler.
This patch reduces overhead, by simply doing a return in such scenarios by
checking the length of current cpu runqueue.
Reviewed-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 6 ++++++
virt/kvm/kvm_main.c | 3 +++
3 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b8c8664..3645458 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -138,6 +138,7 @@ extern int nr_threads;
DECLARE_PER_CPU(unsigned long, process_counts);
extern int nr_processes(void);
extern unsigned long nr_running(void);
+extern unsigned long rq_nr_running(void);
extern unsigned long nr_uninterruptible(void);
extern unsigned long nr_iowait(void);
extern unsigned long nr_iowait_cpu(int cpu);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fbf1fd0..2170b81 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4820,6 +4820,12 @@ void __sched yield(void)
}
EXPORT_SYMBOL(yield);
+unsigned long rq_nr_running(void)
+{
+ return this_rq()->nr_running;
+}
+EXPORT_SYMBOL(rq_nr_running);
+
/**
* yield_to - yield the current processor to another thread in
* your thread group, or accelerate that thread toward the
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 28f00bc..8323685 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1629,6 +1629,9 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
int pass;
int i;
+ if (unlikely(rq_nr_running() == 1))
+ return;
+
kvm_vcpu_set_in_spin_loop(me, true);
/*
* We boost the priority of a VCPU that is runnable but not
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