perf_counter: Add PERF_EVENT_READ

Provide a read() like event which can be used to log the
counter value at specific sites such as child->parent
folding on exit.

In order to be useful, we log the counter parent ID, not the
actual counter ID, since userspace can only relate parent
IDs to perf_counter_attr constructs.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 68 insertions, 4 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 02994a719e27..a72c20e91953 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -2624,6 +2624,66 @@ static void perf_counter_output(struct perf_counter *counter, int nmi,
 }
 
 /*
+ * read event
+ */
+
+struct perf_read_event {
+        struct perf_event_header        header;
+
+        u32                             pid;
+        u32                             tid;
+        u64                             value;
+        u64                             format[3];
+};
+
+static void
+perf_counter_read_event(struct perf_counter *counter,
+                        struct task_struct *task)
+{
+        struct perf_output_handle handle;
+        struct perf_read_event event = {
+                .header = {
+                        .type = PERF_EVENT_READ,
+                        .misc = 0,
+                        .size = sizeof(event) - sizeof(event.format),
+                },
+                .pid = perf_counter_pid(counter, task),
+                .tid = perf_counter_tid(counter, task),
+                .value = atomic64_read(&counter->count),
+        };
+        int ret, i = 0;
+
+        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) {
+                event.header.size += sizeof(u64);
+                event.format[i++] = counter->total_time_enabled;
+        }
+
+        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING) {
+                event.header.size += sizeof(u64);
+                event.format[i++] = counter->total_time_running;
+        }
+
+        if (counter->attr.read_format & PERF_FORMAT_ID) {
+                u64 id;
+
+                event.header.size += sizeof(u64);
+                if (counter->parent)
+                        id = counter->parent->id;
+                else
+                        id = counter->id;
+
+                event.format[i++] = id;
+        }
+
+        ret = perf_output_begin(&handle, counter, event.header.size, 0, 0);
+        if (ret)
+                return;
+
+        perf_output_copy(&handle, &event, event.header.size);
+        perf_output_end(&handle);
+}
+
+/*
  * fork tracking
  */
 
@@ -3985,10 +4045,13 @@ static int inherit_group(struct perf_counter *parent_counter,
 }
 
 static void sync_child_counter(struct perf_counter *child_counter,
-                               struct perf_counter *parent_counter)
+                               struct task_struct *child)
 {
+        struct perf_counter *parent_counter = child_counter->parent;
         u64 child_val;
 
+        perf_counter_read_event(child_counter, child);
+
         child_val = atomic64_read(&child_counter->count);
 
         /*
@@ -4017,7 +4080,8 @@ static void sync_child_counter(struct perf_counter *child_counter,
 
 static void
 __perf_counter_exit_task(struct perf_counter *child_counter,
-                         struct perf_counter_context *child_ctx)
+                         struct perf_counter_context *child_ctx,
+                         struct task_struct *child)
 {
         struct perf_counter *parent_counter;
 
@@ -4031,7 +4095,7 @@ __perf_counter_exit_task(struct perf_counter *child_counter,
          * counters need to be zapped - but otherwise linger.
          */
         if (parent_counter) {
-                sync_child_counter(child_counter, parent_counter);
+                sync_child_counter(child_counter, child);
                 free_counter(child_counter);
         }
 }
@@ -4093,7 +4157,7 @@ void perf_counter_exit_task(struct task_struct *child)
 again:
         list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,
                                  list_entry)
-                __perf_counter_exit_task(child_counter, child_ctx);
+                __perf_counter_exit_task(child_counter, child_ctx, child);
 
         /*
          * If the last counter was a group counter, it will have appended all