Perf: Preserving the event across CPU hotunplug/plug and Creation of an event on offine CPU

[Mukesh Ojha]

Hi Peter/All,

This is regarding the discussion happen in the past about 
https://lkml.org/lkml/2018/2/15/1324

Where the exact ask is to allow preserving and creation of events on a 
offline CPU, so that when the CPU
comes online it will start counting.

I had a look at your patch too and resolve crash during while trying to 
create an event on an offline cpu.

In your patch, you seem to disable event when cpu goes offline which is 
exactly deleting the event
from the pmu and add when it comes online, it seems to work.

But, For the purpose of allowing the creation of event while CPU is 
offline is not able to count event while
CPU coming online, for that i did some change, that did work.

Also, I have query about the events which gets destroyed while CPU is 
offline and we need to remove them
once cpu comes online right ? As Raghavendra also queried the same in 
the above thread.

Don't we need a list where we maintain the events which gets destroyed 
while CPU is dead ?
and clean it up when CPU comes online ?

Thanks.
Mukesh