> > On Wed, Jan 18, 2017 at 08:21:02AM -0500, [email protected] wrote: > > From: Kan Liang <[email protected]> > > > > perf brings additional overhead when monitoring the task which > > frequently generates child task. > > > > When inheriting a event from parent task to child task, the > > sample_period of original parent event (parent_event->parent) will be > > assigned to child event as its initial period, which is usually the > > default sample_period 1. > > > Why is that mostly 1? I would expect the parent event's sample_period to > ramp up as well.
The conclusion is based on the observation in the specific test case mentioned in the description. The sample_period is for the original parent event (parent_event->parent), not the direct parent. I did several tests these days, it can be 100% reproduced by this particular test case in multiplexing. I think the reason is that the original parent event is scheduled out shortly and never gets a chance to trigger interrupt in the first round. So its sample_period doesn't get updated. Then the test case repeatedly generates child tasks and child events. The new child events will be scheduled in/out continually. The original parent event never gets a change to be scheduled again. So the original parent event's sample_period is kept1. Thanks, Kan
