Commit 3fcd6a23 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul 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>
parent f4deaf90

arch/x86/kernel/cpu/aperfmperf.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

	}

include/linux/rcutiny.h

+2 −0
Original line number Diff line number Diff line
@@ -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)

{

include/linux/rcutree.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

kernel/rcu/tree.c

+8 −0
Original line number Diff line number Diff line
@@ -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

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