Re: [PATCH v4 1/5] tracing: Introduce faultable tracepoints

[Peter Zijlstra]

On Tue, Nov 21, 2023 at 07:58:40AM -0800, Paul E. McKenney wrote:

> Tasks Trace RCU allows general blocking in its readers, not just the
> subject-to-priority-boosting blocking permitted within preemptible RCU
> readers.  Restrictions on the use of Tasks Trace RCU are in place to allow
> getting away with this general blocking.  Even systems generously endowed
> with memory are not going to do well when the RCU grace period is blocked
> on I/O, especially if that I/O is across a network to a slow file server.
> 
> Which means a separate RCU instance is needed.  Which is Tasks Trace RCU.

Separate instance not a problem, nor really the question.

What is the basic mechanism of task-tracing? Is it really the existing
tasks-rcu extended with read-side critical sections and call_rcu ?

If so, then why not have it be tasks-rcu?

Or is it a variant of the preemptible/SRCU class of RCUs that are
counter-array based? I suspect not.

So once again, what exactly is tasks-tracing ?