From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: rostedt <rostedt@goodmis.org>
Cc: Joel Fernandes <joelaf@google.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Namhyung Kim <namhyung@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Tom Zanussi <tom.zanussi@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Boqun Feng <boqun.feng@gmail.com>, fweisbec <fweisbec@gmail.com>,
Randy Dunlap <rdunlap@infradead.org>,
kbuild test robot <fengguang.wu@intel.com>,
baohong liu <baohong.liu@intel.com>,
vedang patel <vedang.patel@intel.com>,
kernel-team <kernel-team@lge.com>
Subject: Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
Date: Thu, 26 Apr 2018 11:03:02 -0400 (EDT) [thread overview]
Message-ID: <1609895968.1947.1524754982656.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20180425185149.64f89922@vmware.local.home>
----- On Apr 25, 2018, at 6:51 PM, rostedt rostedt@goodmis.org wrote:
> On Wed, 25 Apr 2018 17:40:56 -0400 (EDT)
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
>
>> One problem with your approach is that you can have multiple callers
>> for the same tracepoint name, where some could be non-preemptible and
>> others blocking. Also, there is then no clear way for the callback
>> registration API to enforce whether the callback expects the tracepoint
>> to be blocking or non-preemptible. This can introduce hard to diagnose
>> issues in a kernel without debug options enabled.
>
> I agree that it should not be tied to an implementation name. But
> "blocking" is confusing. I would say "can_sleep" or some such name that
> states that the trace point caller is indeed something that can sleep.
"trace_*event*_{can,might,may}_sleep" are all acceptable candidates for
me.
>
>>
>> Regarding the name, I'm OK with having something along the lines of
>> trace_*event*_blocking or such. Please don't use "srcu" or other naming
>> that is explicitly tied to the underlying mechanism used internally
>> however: what we want to convey is that this specific tracepoint probe
>> can be preempted and block. The underlying implementation could move to
>> a different RCU flavor brand in the future, and it should not impact
>> users of the tracepoint APIs.
>>
>> In order to ensure that probes that may block only register themselves
>> to tracepoints that allow blocking, we should introduce new tracepoint
>> declaration/definition *and* registration APIs also contain the
>> "BLOCKING/blocking" keywords (or such), so we can ensure that a
>> tracepoint probe being registered to a "blocking" tracepoint is indeed
>> allowed to block.
>
> I'd really don't want to add more declaration/definitions, as we
> already have too many as is, and with different meanings and the number
> is of incarnations is n! in growth.
>
> I'd say we just stick with a trace_<event>_can_sleep() call, and make
> sure that if that is used that no trace_<event>() call is also used, and
> enforce this with linker or compiler tricks.
My main concern is not about having both trace_<event>_can_sleep() mixed
with trace_<event>() calls. It's more about having a registration API allowing
modules registering probes that may need to sleep to explicitly declare it,
and enforce that tracepoint never connects a probe that may need to sleep
with an instrumentation site which cannot sleep.
I'm unsure what's the best way to achieve this goal though. We could possibly
extend the tracepoint_probe_register_* APIs to introduce e.g.
tracepoint_probe_register_prio_flags() and provide a TRACEPOINT_PROBE_CAN_SLEEP
as parameter upon registration. If this flag is provided, then we could figure out
an way to iterate on all callers, and ensure they are all "can_sleep" type of
callers.
Thoughts ?
Thanks,
Mathieu
>
> -- Steve
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2018-04-26 15:03 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-17 4:07 [RFC v4 0/4] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-04-17 4:07 ` [RFC v4 1/4] tracepoint: Add API to not do lockdep checks during RCU ops Joel Fernandes
2018-04-17 4:07 ` [RFC v4 2/4] softirq: reorder trace_softirqs_on to prevent lockdep splat Joel Fernandes
2018-04-17 4:07 ` [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can Joel Fernandes
2018-04-18 9:02 ` Masami Hiramatsu
2018-04-19 5:43 ` Namhyung Kim
2018-04-20 7:07 ` Joel Fernandes
2018-04-23 1:14 ` Joel Fernandes
2018-04-23 3:19 ` Paul E. McKenney
2018-04-23 14:31 ` Mathieu Desnoyers
2018-04-23 14:53 ` Steven Rostedt
2018-04-23 14:59 ` Mathieu Desnoyers
2018-04-23 15:12 ` Paul E. McKenney
2018-04-23 16:18 ` Steven Rostedt
2018-04-23 17:12 ` Mathieu Desnoyers
2018-04-23 17:24 ` Joel Fernandes
2018-04-23 21:22 ` Steven Rostedt
2018-04-24 15:56 ` Paul E. McKenney
2018-04-24 16:01 ` Joel Fernandes
2018-04-24 17:26 ` Paul E. McKenney
2018-04-24 18:23 ` Paul E. McKenney
2018-04-24 18:26 ` Paul E. McKenney
2018-04-24 18:59 ` Joel Fernandes
2018-04-24 19:01 ` Joel Fernandes
2018-04-24 19:09 ` Paul E. McKenney
2018-04-24 19:16 ` Joel Fernandes
2018-04-24 23:21 ` Mathieu Desnoyers
2018-04-24 23:46 ` Joel Fernandes
2018-04-25 0:10 ` Paul E. McKenney
2018-04-25 4:20 ` Paul E. McKenney
2018-04-25 21:27 ` Joel Fernandes
2018-04-25 21:35 ` Paul E. McKenney
2018-04-25 21:40 ` Mathieu Desnoyers
2018-04-25 22:51 ` Steven Rostedt
2018-04-26 15:03 ` Mathieu Desnoyers [this message]
2018-04-26 16:08 ` Mathieu Desnoyers
2018-04-25 23:13 ` Joel Fernandes
2018-04-26 15:13 ` Mathieu Desnoyers
2018-04-26 15:20 ` Joel Fernandes
2018-04-26 15:49 ` Paul E. McKenney
2018-04-23 15:49 ` Joel Fernandes
2018-04-26 2:18 ` Joel Fernandes
2018-05-01 1:18 ` Joel Fernandes
2018-04-17 4:07 ` [RFC v4 4/4] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
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