From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable()
Date: Fri, 7 Apr 2017 10:58:26 -0400 [thread overview]
Message-ID: <20170407105826.562b2e24@gandalf.local.home> (raw)
In-Reply-To: <20170407144334.GT1600@linux.vnet.ibm.com>
On Fri, 7 Apr 2017 07:43:35 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> On Fri, Apr 07, 2017 at 10:01:06AM -0400, Steven Rostedt wrote:
> > Paul,
> >
> > Here's my latest. You OK with it?
>
> Given your update to 3/5, I suspect that we could live with it. I am
> expecting some complaints about increases in idle-entry latency, but might
> be best to wait for complaints rather than complexifying too proactively.
We only added a this_cpu_inc() and this_cpu_dec() which are very fast
operations. I highly doubt it will be measurable. Although, I'm talking
about x86, IIRC, the this_cpu_inc/dec were be poorly written for other
archs in the past. I'm not sure if that was fixed though.
>
> That said, there isn't supposed to be any tracing during the now very
> small interval where RCU's idle-entry is incomplete. Mightn't it be
> better to (under CONFIG_PROVE_RCU or some such) give splats if tracing
> showed up in that interval?
>
Again, tracing is not the issue. I do function tracing in that location
without any problems. The issue here was the stack tracer.
Maybe we can create a new variable that is more cache local to the RCU
code.
What about calling it "rcu_disabled"? Then tracing that depends on RCU
can simply check that.
s/stack_trace_disable/disable_rcu/
s/stack_trace_enable/enable_rcu/
export a per cpu variable rcu_disabled
Then I can have the stack tracer check that variable as well. And we
could even put in a WARN_ON(this_cpu_read(rcu_disabled) in the
TRACE_EVENT() macros.
Thoughts?
-- Steve
next prev parent reply other threads:[~2017-04-07 14:58 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-07 14:01 [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable() Steven Rostedt
2017-04-07 14:01 ` [PATCH 1/5 v2] ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines Steven Rostedt
2017-04-07 14:01 ` [PATCH 2/5 v2] tracing: Replace the per_cpu() with this_cpu() in trace_stack.c Steven Rostedt
2017-04-07 14:36 ` Paul E. McKenney
2017-04-07 14:48 ` Steven Rostedt
2017-04-07 15:08 ` Paul E. McKenney
2017-04-07 14:01 ` [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions Steven Rostedt
2017-04-07 14:22 ` Steven Rostedt
2017-04-07 14:25 ` [PATCH 3/5 v2.1] " Steven Rostedt
2017-04-07 14:01 ` [PATCH 4/5 v2] tracing: Rename trace_active to disable_stack_tracer and inline its modification Steven Rostedt
2017-04-07 14:01 ` [PATCH 5/5 v2] rcu: Fix dyntick-idle tracing Steven Rostedt
2017-04-07 14:40 ` Paul E. McKenney
2017-04-07 14:53 ` Steven Rostedt
2017-04-07 15:09 ` Paul E. McKenney
2017-04-07 15:29 ` Steven Rostedt
2017-04-07 14:43 ` [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable() Paul E. McKenney
2017-04-07 14:58 ` Steven Rostedt [this message]
2017-04-07 15:11 ` Paul E. McKenney
2017-04-07 15:28 ` Steven Rostedt
2017-04-07 16:35 ` [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when rcu_irq_enter() will not work Steven Rostedt
2017-04-07 16:42 ` Paul E. McKenney
2017-04-07 16:44 ` Steven Rostedt
2017-04-07 16:53 ` Paul E. McKenney
2017-04-07 17:03 ` [PATCH 6/5 v2] rcu/tracing: " Steven Rostedt
2017-04-07 17:15 ` Paul E. McKenney
2017-04-07 17:06 ` [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events Steven Rostedt
2017-04-07 17:15 ` Paul E. McKenney
2017-04-07 17:19 ` Mathieu Desnoyers
2017-04-07 17:26 ` Steven Rostedt
2017-04-07 17:32 ` Steven Rostedt
2017-04-07 17:49 ` Mathieu Desnoyers
2017-04-07 17:55 ` Steven Rostedt
2017-04-07 18:10 ` [PATCH 7/5 v3] " Steven Rostedt
2017-04-07 18:17 ` Mathieu Desnoyers
2017-04-07 19:41 ` [PATCH 7/5 v4] " Steven Rostedt
2017-04-07 19:43 ` Steven Rostedt
2017-04-10 17:11 ` Mathieu Desnoyers
2017-04-07 17:28 ` [PATCH 7/5] " Steven Rostedt
2017-04-07 17:48 ` [PATCH 7/5 v2] " Steven Rostedt
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