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

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Message-ID: <045efa69-f0a4-4f04-b092-96b317865cf3@paulmck-laptop>
Date:   Tue, 21 Nov 2023 08:43:27 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.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 11:11:57AM -0500, Mathieu Desnoyers wrote:
> On 2023-11-21 11:07, Steven Rostedt wrote:
> > On Tue, 21 Nov 2023 11:00:13 -0500
> > Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> > 
> > > > tasks-tracing-rcu:
> > > >     extention of tasks to have critical-sections ? Should this simply be
> > > >     tasks?
> > > 
> > > tasks-trace-rcu is meant to allow tasks to block/take a page fault
> > > within the read-side. It is specialized for tracing and has a single
> > > domain. It does not need the smp_mb on the read-side, which makes it
> > > lower-overhead than SRCU.
> > 
> > IOW, task-trace-rcu allows the call to schedule in its critical section,
> > whereas task-rcu does not?
> 
> Correct.
> 
> And unlike preemptible rcu, tasks-trace-rcu allows calls to schedule which
> do not provide priority inheritance guarantees (such as I/O triggered by
> page faults).

But please keep it to things allowed in vanilla RCU read-side critical
sections and I/O triggered by page faults.  If you need something else,
that is a discussion between all the current users of RCU Tasks Trace.

							Thanx, Paul