On Mon, Feb 12, 2018 at 10:04:42PM +0100, Jiri Olsa wrote: > On Mon, Feb 12, 2018 at 09:42:05AM -0800, Raghavendra Rao Ananta wrote: > > Hi Jiri, > > > > Thank you for the response. > > > > Does perf tool has its own check to see if the CPU was offline during the > > lifetime of an event? If so, it might ignore these type of events. > > nope, we don't check on that > > > > > Initially, I tested the same using perf tool and found similar results. > > Then I debugged further and found that the perf core was actually sending > > data to the userspace (copy_to_user()) and the corresponding count for the > > data. Hence, I tested this further by writing my own userspace application, > > and I was able to read the count through this, > > even when the CPU was made offline and back online. > > > > Do you think we also have to modify the perf tool accordingly? > > hum, I wonder what's wrong.. will check
I think the user space needs to enable the event once the cpu gets online.. which we dont do and your app does..? maybe we could add perf_event_attr::enable_on_online ;-) I'll check what we can do in user space, I guess we can monitor the cpu state and enable event accordingly jirka