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>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index bcbf1c4..6a384f0 100644 (file)
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -335,6 +335,18 @@ enum perf_event_type {
        PERF_EVENT_FORK                 = 7,
 
        /*
+        * struct {
+        *      struct perf_event_header        header;
+        *      u32                             pid, tid;
+        *      u64                             value;
+        *      { u64           time_enabled;   } && PERF_FORMAT_ENABLED
+        *      { u64           time_running;   } && PERF_FORMAT_RUNNING
+        *      { u64           parent_id;      } && PERF_FORMAT_ID
+        * };
+        */
+       PERF_EVENT_READ                 = 8,
+
+       /*
         * When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
         * will be PERF_SAMPLE_*
         *

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 02994a7..a72c20e 100644 (file)
--- 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