The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 3fcd6a230fa7d03bffcb831a81b40435c146c12b
Gitweb: https://git.kernel.org/tip/3fcd6a230fa7d03bffcb831a81b40435c146c12b
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Thu, 03 Sep 2020 15:23:29 -07:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Fri, 06 Nov 2020 16:59:11 -08:00
x86/cpu: Avoid cpuinfo-induced IPIing of idle CPUs
Currently, accessing /proc/cpuinfo sends IPIs to idle CPUs in order to
learn their clock frequency. Which is a bit strange, given that waking
them from idle likely significantly changes their clock frequency.
This commit therefore avoids sending /proc/cpuinfo-induced IPIs to
idle CPUs.
[ paulmck: Also check for idle in arch_freq_prepare_all(). ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: <x86@xxxxxxxxxx>
---
arch/x86/kernel/cpu/aperfmperf.c | 6 ++++++
include/linux/rcutiny.h | 2 ++
include/linux/rcutree.h | 1 +
kernel/rcu/tree.c | 8 ++++++++
4 files changed, 17 insertions(+)
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index dd3261d..22911de 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -14,6 +14,7 @@
#include <linux/cpufreq.h>
#include <linux/smp.h>
#include <linux/sched/isolation.h>
+#include <linux/rcupdate.h>
#include "cpu.h"
@@ -93,6 +94,9 @@ unsigned int aperfmperf_get_khz(int cpu)
if (!housekeeping_cpu(cpu, HK_FLAG_MISC))
return 0;
+ if (rcu_is_idle_cpu(cpu))
+ return 0; /* Idle CPUs are completely uninteresting. */
+
aperfmperf_snapshot_cpu(cpu, ktime_get(), true);
return per_cpu(samples.khz, cpu);
}
@@ -112,6 +116,8 @@ void arch_freq_prepare_all(void)
for_each_online_cpu(cpu) {
if (!housekeeping_cpu(cpu, HK_FLAG_MISC))
continue;
+ if (rcu_is_idle_cpu(cpu))
+ continue; /* Idle CPUs are completely uninteresting. */
if (!aperfmperf_snapshot_cpu(cpu, now, false))
wait = true;
}
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 7c1ecdb..2a97334 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -89,6 +89,8 @@ static inline void rcu_irq_enter_irqson(void) { }
static inline void rcu_irq_exit(void) { }
static inline void rcu_irq_exit_preempt(void) { }
static inline void rcu_irq_exit_check_preempt(void) { }
+#define rcu_is_idle_cpu(cpu) \
+ (is_idle_task(current) && !in_nmi() && !in_irq() && !in_serving_softirq())
static inline void exit_rcu(void) { }
static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 59eb5cd..df578b7 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -50,6 +50,7 @@ void rcu_irq_exit(void);
void rcu_irq_exit_preempt(void);
void rcu_irq_enter_irqson(void);
void rcu_irq_exit_irqson(void);
+bool rcu_is_idle_cpu(int cpu);
#ifdef CONFIG_PROVE_RCU
void rcu_irq_exit_check_preempt(void);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 06895ef..1d84c0b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -341,6 +341,14 @@ static bool rcu_dynticks_in_eqs(int snap)
return !(snap & RCU_DYNTICK_CTRL_CTR);
}
+/* Return true if the specified CPU is currently idle from an RCU viewpoint. */
+bool rcu_is_idle_cpu(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
+}
+
/*
* Return true if the CPU corresponding to the specified rcu_data
* structure has spent some time in an extended quiescent state since
|