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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: rostedt <rostedt@goodmis.org>, Joel Fernandes <joelaf@google.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: Mon, 23 Apr 2018 08:12:22 -0700	[thread overview]
Message-ID: <20180423151222.GO26088@linux.vnet.ibm.com> (raw)
In-Reply-To: <1045420715.14686.1524495583859.JavaMail.zimbra@efficios.com>

On Mon, Apr 23, 2018 at 10:59:43AM -0400, Mathieu Desnoyers wrote:
> ----- On Apr 23, 2018, at 10:53 AM, rostedt rostedt@goodmis.org wrote:
> 
> > On Mon, 23 Apr 2018 10:31:28 -0400 (EDT)
> > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> > 
> >> I've been wanting to introduce an alternative tracepoint instrumentation
> >> "flavor" for e.g. system call entry/exit which rely on SRCU rather than
> >> sched-rcu (preempt-off). This would allow taking faults within the
> >> instrumentation
> >> probe, which makes lots of things easier when fetching data from user-space
> >> upon system call entry/exit. This could also be used to cleanly instrument
> >> the idle loop.
> > 
> > I'd be OK with such an approach. And I don't think it would be that
> > hard to implement. It could be similar to the rcu_idle() tracepoints,
> > where each flavor simply passes in what protection it uses for
> > DO_TRACE(). We could do linker tricks to tell the tracepoint.c code how
> > the tracepoint is protected (add section code, that could be read to
> > update flags in the tracepoint). Of course modules that have
> > tracepoints could only use the standard preempt ones.
> > 
> > That is, if trace_##event##_srcu(trace_##event##_sp, PARAMS), is used,
> > then the trace_##event##_sp would need to be created somewhere. The use
> > of trace_##event##_srcu() would create a section entry, and on boot up
> > we can see that the use of this tracepoint requires srcu protection
> > with a pointer to the trace_##event##_sp srcu_struct. This could be
> > used to make sure that trace_#event() call isn't done multiple times
> > that uses two different protection flavors.
> > 
> > I'm just brain storming the idea, and I'm sure I screwed up something
> > above, but I do believe it is feasible.
> 
> The main open question here is whether we want one SRCU grace period
> domain per SRCU tracepoint definition, or just one SRCU domain for all
> SRCU tracepoints would be fine.
> 
> I'm not sure what we would gain by having the extra granularity provided
> by one SRCU grace period domain per tracepoint, and having a single SRCU
> domain for all SRCU tracepoints makes it easy to batch grace period after
> bulk tracepoint modifications.

I don't see how having multiple SRCU domains would help anything, but
perhaps I am missing something basic.

							thanx, Paul

  reply	other threads:[~2018-04-23 15:11 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 [this message]
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
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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