From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Christoph Lameter <cl@linux.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Chris Metcalf <cmetcalf@tilera.com>,
Geoff Levand <geoff@infradead.org>,
Gilad Ben Yossef <gilad@benyossef.com>,
Hakan Akkan <hakanakkan@gmail.com>,
Kevin Hilman <khilman@linaro.org>,
Li Zhong <zhong@linux.vnet.ibm.com>,
Oleg Nesterov <oleg@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/2] nohz: Add basic tracing
Date: Tue, 23 Apr 2013 14:01:56 -0700 [thread overview]
Message-ID: <20130423210156.GD3427@linux.vnet.ibm.com> (raw)
In-Reply-To: <1366747223.9609.163.camel@gandalf.local.home>
On Tue, Apr 23, 2013 at 04:00:23PM -0400, Steven Rostedt wrote:
> On Tue, 2013-04-23 at 18:12 +0000, Christoph Lameter wrote:
> > On Mon, 22 Apr 2013, Frederic Weisbecker wrote:
> >
> > > It's not obvious to find out why the full dynticks subsystem
> > > doesn't always stop the tick: whether this is due to kthreads,
> > > posix timers, perf events, etc...
> > >
> > > These new tracepoints are here to help the user diagnose
> > > the failures and test this feature.
> >
> > Very good. This will help a lot.
>
> You can also do:
>
> cd /sys/kernel/debug/tracing
> echo 1 > max_graph_depth
> echo function_graph > current_tracer
>
> And then run your code, and look to see what happens on the cpu in
> question:
>
> cat per_cpu/cpuX/trace
>
> The "max_graph_depth" of one will make the function graph tracer just
> trace the first function that enters the kernel. You'll be able to see
> if the kernel did anything to your userspace application that wasn't
> planned.
>
> "max_graph_depth" was added in 3.9-rc1
Very cool! I have added this to the documentation.
Thanx, Paul
prev parent reply other threads:[~2013-04-23 21:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-22 21:08 [GIT PULL] nohz: Help for testing Frederic Weisbecker
2013-04-22 21:08 ` [PATCH 1/2] nohz: Select wide RCU nocb for full dynticks Frederic Weisbecker
2013-04-22 21:08 ` [PATCH 2/2] nohz: Add basic tracing Frederic Weisbecker
2013-04-23 18:12 ` Christoph Lameter
2013-04-23 20:00 ` Steven Rostedt
2013-04-23 21:01 ` Paul E. McKenney [this message]
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