When monitoring another process, the kernels up through linux-2.6.34-rc7
have a bug where all of the events except the group leader give a zero
value for the time_running and time_enabled values. This #define allows
us to work around that bug by copying these two values from the group
leader to all of its siblings.
Signed-off-by: Corey Ashford <cjash...@linux.vnet.ibm.com>
diff --git a/perf_examples/task.c b/perf_examples/task.c
index 75de973..35ba0b8 100644
--- a/perf_examples/task.c
+++ b/perf_examples/task.c
@@ -61,6 +61,15 @@ child(char **arg)
/* not reached */
}
+/*
+ * When monitoring another process, the kernels up through linux-2.6.34-rc7
+ * have a bug where all of the events except the group leader give a zero
+ * value for the time_running and time_enabled values. This #define allows
+ * us to work around that bug by copying these two values from the group
+ * leader to all of its siblings.
+ */
+#define KERNEL_HAS_GROUP_SCALING_BUG 1
+
static void
read_groups(perf_event_desc_t *fds, int num)
{
@@ -120,6 +129,16 @@ read_groups(perf_event_desc_t *fds, int num)
* thus may be multiplexed
*/
fds[i].prev_value = fds[i].value;
+#if KERNEL_HAS_GROUP_SCALING_BUG
+ /* only the group leader has non-zero
+ enabled and running values */
+ if (fds[i].group_leader != i) {
+ /* copy the correct values from the group
+ leader */
+ values[1] = fds[fds[i].group_leader].enabled;
+ values[2] = fds[fds[i].group_leader].running;
+ }
+#endif
fds[i].value = perf_scale(values);
fds[i].enabled = values[1];
fds[i].running = values[2];
------------------------------------------------------------------------------
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