perf_counter: Generic per counter interrupt throttle

Introduce a generic per counter interrupt throttle.

This uses the perf_counter_overflow() quick disable to throttle a specific
counter when its going too fast when a pmu->unthrottle() method is provided
which can undo the quick disable.

Power needs to implement both the quick disable and the unthrottle method.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <20090525153931.703093461@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 63 insertions, 4 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 14b1fe984832..ec9c4007a7f9 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -46,6 +46,7 @@ static atomic_t nr_comm_tracking __read_mostly;
 
 int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
 int sysctl_perf_counter_mlock __read_mostly = 512; /* 'free' kb per user */
+int sysctl_perf_counter_limit __read_mostly = 100000; /* max NMIs per second */
 
 /*
  * Lock for (sysadmin-configurable) counter reservations:
@@ -1066,12 +1067,15 @@ static void perf_counter_cpu_sched_in(struct perf_cpu_context *cpuctx, int cpu)
         __perf_counter_sched_in(ctx, cpuctx, cpu);
 }
 
+#define MAX_INTERRUPTS (~0ULL)
+
+static void perf_log_throttle(struct perf_counter *counter, int enable);
 static void perf_log_period(struct perf_counter *counter, u64 period);
 
 static void perf_adjust_freq(struct perf_counter_context *ctx)
 {
         struct perf_counter *counter;
-        u64 irq_period;
+        u64 interrupts, irq_period;
         u64 events, period;
         s64 delta;
 
@@ -1080,10 +1084,19 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
                 if (counter->state != PERF_COUNTER_STATE_ACTIVE)
                         continue;
 
+                interrupts = counter->hw.interrupts;
+                counter->hw.interrupts = 0;
+
+                if (interrupts == MAX_INTERRUPTS) {
+                        perf_log_throttle(counter, 1);
+                        counter->pmu->unthrottle(counter);
+                        interrupts = 2*sysctl_perf_counter_limit/HZ;
+                }
+
                 if (!counter->hw_event.freq || !counter->hw_event.irq_freq)
                         continue;
 
-                events = HZ * counter->hw.interrupts * counter->hw.irq_period;
+                events = HZ * interrupts * counter->hw.irq_period;
                 period = div64_u64(events, counter->hw_event.irq_freq);
 
                 delta = (s64)(1 + period - counter->hw.irq_period);
@@ -1097,7 +1110,6 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
                 perf_log_period(counter, irq_period);
 
                 counter->hw.irq_period = irq_period;
-                counter->hw.interrupts = 0;
         }
         spin_unlock(&ctx->lock);
 }
@@ -2544,6 +2556,35 @@ static void perf_log_period(struct perf_counter *counter, u64 period)
 }
 
 /*
+ * IRQ throttle logging
+ */
+
+static void perf_log_throttle(struct perf_counter *counter, int enable)
+{
+        struct perf_output_handle handle;
+        int ret;
+
+        struct {
+                struct perf_event_header        header;
+                u64                             time;
+        } throttle_event = {
+                .header = {
+                        .type = PERF_EVENT_THROTTLE + 1,
+                        .misc = 0,
+                        .size = sizeof(throttle_event),
+                },
+                .time = sched_clock(),
+        };
+
+        ret = perf_output_begin(&handle, counter, sizeof(throttle_event), 0, 0);
+        if (ret)
+                return;
+
+        perf_output_put(&handle, throttle_event);
+        perf_output_end(&handle);
+}
+
+/*
  * Generic counter overflow handling.
  */
 
@@ -2551,9 +2592,19 @@ int perf_counter_overflow(struct perf_counter *counter,
                           int nmi, struct pt_regs *regs, u64 addr)
 {
         int events = atomic_read(&counter->event_limit);
+        int throttle = counter->pmu->unthrottle != NULL;
         int ret = 0;
 
-        counter->hw.interrupts++;
+        if (!throttle) {
+                counter->hw.interrupts++;
+        } else if (counter->hw.interrupts != MAX_INTERRUPTS) {
+                counter->hw.interrupts++;
+                if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
+                        counter->hw.interrupts = MAX_INTERRUPTS;
+                        perf_log_throttle(counter, 0);
+                        ret = 1;
+                }
+        }
 
         /*
          * XXX event_limit might not quite work as expected on inherited
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 3cb1849f5989..0c4bf863afa3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -930,6 +930,14 @@ static struct ctl_table kern_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,
         },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_int_limit",
+                .data           = &sysctl_perf_counter_limit,
+                .maxlen         = sizeof(sysctl_perf_counter_limit),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
 #endif
 /*
  * NOTE: do not add new entries to this table unless you have read