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Commit 1b023a96 authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
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perfcounters: throttle on too high IRQ rates 



Starting kerneltop with only -c 100 seems to be a bad idea, it can
easily lock the system due to perfcounter IRQ overload.

So add throttling: if a new IRQ arrives in a shorter than
PERFMON_MIN_PERIOD_NS time, turn off perfcounters and untrottle them
from the next timer tick.

Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 05e3423c

arch/x86/kernel/apic.c

+2 −0
Original line number Diff line number Diff line
@@ -781,6 +781,8 @@ static void local_apic_timer_interrupt(void) 
	inc_irq_stat(apic_timer_irqs);



	evt->event_handler(evt);



	perf_counter_unthrottle();

}



/*

arch/x86/kernel/cpu/perf_counter.c

+32 −6
Original line number Diff line number Diff line
@@ -33,6 +33,9 @@ static int nr_counters_fixed __read_mostly; 
struct cpu_hw_counters {

	struct perf_counter	*counters[X86_PMC_IDX_MAX];

	unsigned long		used[BITS_TO_LONGS(X86_PMC_IDX_MAX)];

	u64			last_interrupt;

	u64			global_enable;

	int			throttled;

};



/*
@@ -474,16 +477,19 @@ perf_handle_group(struct perf_counter *sibling, u64 *status, u64 *overflown) 
static void __smp_perf_counter_interrupt(struct pt_regs *regs, int nmi)

{

	int bit, cpu = smp_processor_id();

	u64 ack, status, saved_global;

	struct cpu_hw_counters *cpuc;

	u64 ack, status, now;

	struct cpu_hw_counters *cpuc = &per_cpu(cpu_hw_counters, cpu);



	rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, saved_global);

	rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);



	/* Disable counters globally */

	wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0);

	ack_APIC_irq();



	cpuc = &per_cpu(cpu_hw_counters, cpu);

	now = sched_clock();

	if (now - cpuc->last_interrupt < PERFMON_MIN_PERIOD_NS)

		cpuc->throttled = 1;

	cpuc->last_interrupt = now;



	rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, status);

	if (!status)
@@ -533,9 +539,29 @@ static void __smp_perf_counter_interrupt(struct pt_regs *regs, int nmi) 
		goto again;

out:

	/*

	 * Restore - do not reenable when global enable is off:

	 * Restore - do not reenable when global enable is off or throttled:

	 */

	wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, saved_global);

	if (!cpuc->throttled)

		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);

}



void perf_counter_unthrottle(void)

{

	struct cpu_hw_counters *cpuc;



	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON))

		return;



	if (unlikely(!perf_counters_initialized))

		return;



	cpuc = &per_cpu(cpu_hw_counters, smp_processor_id());

	if (cpuc->throttled) {

		if (printk_ratelimit())

			printk(KERN_WARNING "PERFMON: max event frequency exceeded!\n");

		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);

		cpuc->throttled = 0;

	}

}



void smp_perf_counter_interrupt(struct pt_regs *regs)

include/linux/perf_counter.h

+4 −0
Original line number Diff line number Diff line
@@ -254,6 +254,7 @@ extern void perf_counter_init_task(struct task_struct *child); 
extern void perf_counter_exit_task(struct task_struct *child);

extern void perf_counter_notify(struct pt_regs *regs);

extern void perf_counter_print_debug(void);

extern void perf_counter_unthrottle(void);

extern u64 hw_perf_save_disable(void);

extern void hw_perf_restore(u64 ctrl);

extern int perf_counter_task_disable(void);
@@ -270,6 +271,8 @@ static inline int is_software_counter(struct perf_counter *counter) 
	return !counter->hw_event.raw && counter->hw_event.type < 0;

}



#define PERFMON_MIN_PERIOD_NS 10000



#else

static inline void

perf_counter_task_sched_in(struct task_struct *task, int cpu)		{ }
@@ -281,6 +284,7 @@ static inline void perf_counter_init_task(struct task_struct *child) { } 
static inline void perf_counter_exit_task(struct task_struct *child)	{ }

static inline void perf_counter_notify(struct pt_regs *regs)		{ }

static inline void perf_counter_print_debug(void)			{ }

static inline void perf_counter_unthrottle(void)			{ }

static inline void hw_perf_restore(u64 ctrl)			{ }

static inline u64 hw_perf_save_disable(void)		      { return 0; }

static inline int perf_counter_task_disable(void)	{ return -EINVAL; }