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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@kernel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <x86@kernel.org>
zero-sugar-mainline-defconfig
Paul E. McKenney 2020-09-03 15:23:29 -07:00
parent f4deaf9021
commit 3fcd6a230f
4 changed files with 17 additions and 0 deletions
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6
arch/x86/kernel/cpu/aperfmperf.c
View File

@ -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;
}

2
include/linux/rcutiny.h
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@ -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)
{

1
include/linux/rcutree.h
View File

@ -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);

8
kernel/rcu/tree.c
View File

@ -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