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Message-ID: <017aff1d-70cc-4c0c-a05c-aad4329068e7@paulmck-laptop>
Date: Tue, 21 Nov 2023 08:46:28 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org,
Michael Jeanson <mjeanson@...icios.com>,
Alexei Starovoitov <ast@...nel.org>,
Yonghong Song <yhs@...com>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>, bpf@...r.kernel.org,
Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v4 1/5] tracing: Introduce faultable tracepoints
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
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