perf_counter: Log irq_period changes

For the dynamic irq_period code, log whenever we change the period so that
analyzing code can normalize the event flow.

[ Impact: add new feature to allow more precise profiling ]

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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <20090520102553.298769743@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 47 insertions, 1 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index c8c1dfc22c93..f612941ef46e 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -258,6 +258,14 @@ enum perf_event_type {
         PERF_EVENT_COMM                 = 3,
 
         /*
+         * struct {
+         *      struct perf_event_header        header;
+         *      u64                             irq_period;
+         * };
+         */
+        PERF_EVENT_PERIOD               = 4,
+
+        /*
          * When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
          * will be PERF_RECORD_*
          *
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 64113e6d1942..db02eb16c777 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1046,7 +1046,9 @@ int perf_counter_task_enable(void)
         return 0;
 }
 
-void perf_adjust_freq(struct perf_counter_context *ctx)
+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;
@@ -1072,6 +1074,8 @@ void perf_adjust_freq(struct perf_counter_context *ctx)
                 if (!irq_period)
                         irq_period = 1;
 
+                perf_log_period(counter, irq_period);
+
                 counter->hw.irq_period = irq_period;
                 counter->hw.interrupts = 0;
         }
@@ -2407,6 +2411,40 @@ void perf_counter_munmap(unsigned long addr, unsigned long len,
 }
 
 /*
+ *
+ */
+
+static void perf_log_period(struct perf_counter *counter, u64 period)
+{
+        struct perf_output_handle handle;
+        int ret;
+
+        struct {
+                struct perf_event_header        header;
+                u64                             time;
+                u64                             period;
+        } freq_event = {
+                .header = {
+                        .type = PERF_EVENT_PERIOD,
+                        .misc = 0,
+                        .size = sizeof(freq_event),
+                },
+                .time = sched_clock(),
+                .period = period,
+        };
+
+        if (counter->hw.irq_period == period)
+                return;
+
+        ret = perf_output_begin(&handle, counter, sizeof(freq_event), 0, 0);
+        if (ret)
+                return;
+
+        perf_output_put(&handle, freq_event);
+        perf_output_end(&handle);
+}
+
+/*
  * Generic counter overflow handling.
  */