On Thu, Jan 30, 2025 at 03:21:36PM -0500, Steven Rostedt wrote: > Coming back from this. It would be fine if we could do the back trace when > we come back from the scheduler, so it should not be an issue if the task > even has to schedule again to fault in the sframe information.
So there would be two callback hook points: - schedule() after enabling preemption - task work and first one wins? > I was also wondering if the unwinder doesn't keep track of who requested > the back trace, just that someone did. Then it would just take a single > flag in the task struct to do the back trace. Return the "cookie" to the > tracer that requested the back trace, and when you do the back trace, just > call all callbacks with that cookie. Let the tracer decided if it wants to > record the back trace or ignore it based on the cookie. > > That is, the tracers would need to keep track of the cookies that it cares > about, as if there's other tracers asking for stack traces on tasks that > this tracer doesn't care about it needs to handle being called when it > doesn't care about the stack trace. That said, if you want to trace all > tasks, you can just ignore the cookies and record the traces. Easy enough for the unwinder, but IIUC each tracer would have to maintain a global list of pending cookies (and corresponding ptrs to perf_event, trace_array, etc)? Would that not create a lot of contention? Seems like there really needs to be some kind of per-task or per-request state. -- Josh
