linux-kernel - Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace

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Date:   Mon, 23 Apr 2018 17:22:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        fweisbec <fweisbec@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        baohong liu <baohong.liu@...el.com>,
        vedang patel <vedang.patel@...el.com>,
        kernel-team <kernel-team@....com>
Subject: Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you
 can

On Mon, 23 Apr 2018 13:12:21 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

 
> I'm inclined to explicitly declare the tracepoints with their given
> synchronization method. Tracepoint probe callback functions for currently
> existing tracepoints expect to have preemption disabled when invoked.
> This assumption will not be true anymore for srcu-tracepoints.

Actually, why not have a flag attached to the tracepoint_func that
states if it expects preemption to be enabled or not? If a
trace_##event##_srcu() is called, then simply disable preemption before
calling the callbacks for it. That way if a callback is fine for use
with srcu, then it would require calling

	register_trace_##event##_may_sleep();

Then if someone uses this on a tracepoint where preemption is disabled,
we simply do not call it.

-- Steve