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

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Message-ID: <e1d33ff6-bf8d-465f-8626-f692ce4debe5@efficios.com>
Date:   Tue, 21 Nov 2023 11:11:57 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.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 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).

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com