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: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 33ba9fe0a781..91f1ca4c01c0 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -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; }