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

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Message-ID: <20231121155256.GN4779@noisy.programming.kicks-ass.net>
Date:   Tue, 21 Nov 2023 16:52:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        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 03:46:43PM +0100, Peter Zijlstra wrote:

> Why is this such a hard question?

Anyway, recapping from IRC:

preemptible, SRCU:
  counter-array based, GP advances by increasing array index
  and waiting for previous index to drop to 0.

  notably, a GP can pass while a task is preempted but not within a
  critical section.

  SRCU has smp_mb() in the critical sections to improve GP.

tasks:
  waits for every task to pass schedule()

  ensures that any pieces of text rendered unreachable before, is
  actually unused after.

tasks-rude:
  like tasks, but different? build to handle tracing while rcu-idle,
  even though that was already deemed bad?

tasks-tracing-rcu:
  extention of tasks to have critical-sections ? Should this simply be
  tasks?

Can someone complete, please?