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Commit 4ac13294 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

perf counters: protect them against CSTATE transitions 



Impact: fix rare lost events problem

There are CPUs whose performance counters misbehave on CSTATE transitions,
so provide a way to just disable/enable them around deep idle methods.

(hw_perf_enable_all() is cheap on x86.)

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 43874d23

arch/x86/kernel/cpu/perf_counter.c

+13 −1
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ 
#include <linux/notifier.h>

#include <linux/hardirq.h>

#include <linux/kprobes.h>

#include <linux/module.h>

#include <linux/kdebug.h>

#include <linux/sched.h>
@@ -119,10 +120,21 @@ void hw_perf_enable_all(void) 
	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, perf_counter_mask, 0);

}



void hw_perf_disable_all(void)

void hw_perf_restore_ctrl(u64 ctrl)

{

	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, ctrl, 0);

}

EXPORT_SYMBOL_GPL(hw_perf_restore_ctrl);



u64 hw_perf_disable_all(void)

{

	u64 ctrl;



	rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);

	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0, 0);

	return ctrl;

}

EXPORT_SYMBOL_GPL(hw_perf_disable_all);



static inline void

__hw_perf_counter_disable(struct hw_perf_counter *hwc, unsigned int idx)

drivers/acpi/processor_idle.c

+8 −0
Original line number Diff line number Diff line
@@ -270,8 +270,11 @@ static atomic_t c3_cpu_count; 
/* Common C-state entry for C2, C3, .. */

static void acpi_cstate_enter(struct acpi_processor_cx *cstate)

{

	u64 pctrl;



	/* Don't trace irqs off for idle */

	stop_critical_timings();

	pctrl = hw_perf_disable_all();

	if (cstate->entry_method == ACPI_CSTATE_FFH) {

		/* Call into architectural FFH based C-state */

		acpi_processor_ffh_cstate_enter(cstate);
@@ -284,6 +287,7 @@ static void acpi_cstate_enter(struct acpi_processor_cx *cstate) 
		   gets asserted in time to freeze execution properly. */

		unused = inl(acpi_gbl_FADT.xpm_timer_block.address);

	}

	hw_perf_restore_ctrl(pctrl);

	start_critical_timings();

}

#endif /* !CONFIG_CPU_IDLE */
@@ -1425,8 +1429,11 @@ static inline void acpi_idle_update_bm_rld(struct acpi_processor *pr, 
 */

static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)

{

	u64 pctrl;



	/* Don't trace irqs off for idle */

	stop_critical_timings();

	pctrl = hw_perf_disable_all();

	if (cx->entry_method == ACPI_CSTATE_FFH) {

		/* Call into architectural FFH based C-state */

		acpi_processor_ffh_cstate_enter(cx);
@@ -1441,6 +1448,7 @@ static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx) 
		   gets asserted in time to freeze execution properly. */

		unused = inl(acpi_gbl_FADT.xpm_timer_block.address);

	}

	hw_perf_restore_ctrl(pctrl);

	start_critical_timings();

}

include/linux/perf_counter.h

+4 −0
Original line number Diff line number Diff line
@@ -156,6 +156,8 @@ extern void perf_counter_task_tick(struct task_struct *task, int cpu); 
extern void perf_counter_init_task(struct task_struct *task);

extern void perf_counter_notify(struct pt_regs *regs);

extern void perf_counter_print_debug(void);

extern void hw_perf_restore_ctrl(u64 ctrl);

extern u64 hw_perf_disable_all(void);

#else

static inline void

perf_counter_task_sched_in(struct task_struct *task, int cpu)		{ }
@@ -166,6 +168,8 @@ perf_counter_task_tick(struct task_struct *task, int cpu) { } 
static inline void perf_counter_init_task(struct task_struct *task)	{ }

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

static inline void perf_counter_print_debug(void)			{ }

static inline void hw_perf_restore_ctrl(u64 ctrl)			{ }

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

#endif



#endif /* _LINUX_PERF_COUNTER_H */