On Tue, 29 Mar 2016 18:04:01 +0200
Peter Zijlstra [off-list ref] wrote:

On Tue, Mar 29, 2016 at 11:57:00AM -0400, Steven Rostedt wrote:

quoted

Hmm, I probably could add tracing infrastructure that would let us
extend existing tracepoints. That is, without modifying sched_switch,
we could add a new tracepoint that when enabled, would attach itself to
the sched_switch tracepoint and record different information. Like a
special sched_switch_deadline tracepoint, that would record the existing
runtime,deadline and period for deadline tasks. It wont add more
tracepoints into the core scheduler, but use the existing one.  

Urgh; maybe. But I would would not want the new thing to be called
_deadline, maybe _v{n} id anything and have a KERN_WARNING emitted when
people enable the old one.

I wasn't thinking of having a new sched switch, I was thinking of
having multiple ones. And not versions, as the one for a deadline task
wouldn't be applicable for a non deadline task. But regardless, I'm
also thinking of something else.

Ideally we'd rename the old one, but I suspect even that would break
stuff :/

Yes, we don't want to get rid of the old one. But it shouldn't break
anything if we extend it. I'm thinking of extending it with a dynamic
array to store the deadline task values (runtime, period). And for non
deadline tasks, the array would be empty (size zero). I think that
could be doable and maintain backward compatibility.

-- Steve