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

[Paul E. McKenney]

On Tue, Nov 21, 2023 at 05:03:00PM +0100, Peter Zijlstra wrote:
> 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 ?

I think we covered this elsewhere in the thread, but if there are
lingering questions, you know where to find us.  ;-)

							Thanx, Paul