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From: Joel Fernandes <joelaf@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Tom Zanussi <tom.zanussi@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Boqun Feng <boqun.feng@gmail.com>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	"Cc: Frederic Weisbecker" <fweisbec@gmail.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Fenguang Wu <fengguang.wu@intel.com>,
	Baohong Liu <baohong.liu@intel.com>,
	Vedang Patel <vedang.patel@intel.com>,
	"Cc: Android Kernel" <kernel-team@android.com>
Subject: Re: [PATCH RFC v5 5/6] tracepoint: Make rcuidle tracepoint callers use SRCU
Date: Tue, 01 May 2018 16:44:37 +0000	[thread overview]
Message-ID: <CAJWu+oowGDfwWGa6yju4F_qYG_CWh7a4Bk=pnVXuBv0_HjX5nA@mail.gmail.com> (raw)
In-Reply-To: <20180501102401.2cac5781@gandalf.local.home>

On Tue, May 1, 2018 at 7:24 AM Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 30 Apr 2018 18:42:03 -0700
> Joel Fernandes <joelaf@google.com> wrote:

> > In recent tests with IRQ on/off tracepoints, a large performance
> > overhead ~10% is noticed when running hackbench. This is root caused to
> > calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the
> > tracepoint code. Following a long discussion on the list [1] about this,
> > we concluded that srcu is a better alternative for use during rcu idle.
> > Although it does involve extra barriers, its lighter than the sched-rcu
> > version which has to do additional RCU calls to notify RCU idle about
> > entry into RCU sections.
> >
> > In this patch, we change the underlying implementation of the
> > trace_*_rcuidle API to use SRCU. This has shown to improve performance
> > alot for the high frequency irq enable/disable tracepoints.

> Can you post some numbers?


Here are some numbers (which I'll also include in the next series spin):

With a run of the following 30 times on a single core x86 Qemu instance
with 1GB memory:
hackbench -g 4 -f 2 -l 3000

Completion times in seconds. CONFIG_PROVE_LOCKING=y.

No patches (without this series)
Mean: 3.048
Median: 3.025
Std Dev: 0.064

With Lockdep using irq tracepoints with RCU implementation:
Mean: 3.451   (-11.66 %)
Median: 3.447 (-12.22%)
Std Dev: 0.049

With Lockdep using irq tracepoints with SRCU implementation:
Mean: 3.020   (I would consider the improvement against the "without this
series" case as just noise).
Median: 3.013
Std Dev: 0.033

thanks,

- Joel

  parent reply	other threads:[~2018-05-01 16:44 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-01  1:41 [PATCH RFC v5 0/6] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-05-01  1:41 ` [PATCH RFC v5 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat Joel Fernandes
2018-05-01 14:02   ` Steven Rostedt
2018-05-01 15:00     ` Joel Fernandes
2018-05-01  1:42 ` [PATCH RFC v5 2/6] srcu: Add notrace variants of srcu_read_{lock,unlock} Joel Fernandes
2018-05-01 14:04   ` Steven Rostedt
2018-05-01  1:42 ` [PATCH RFC v5 3/6] srcu: Add notrace variant of srcu_dereference Joel Fernandes
2018-05-01 14:06   ` Steven Rostedt
2018-05-01 15:07     ` Joel Fernandes
2018-05-01 14:18   ` Paul E. McKenney
2018-05-01 15:04     ` Steven Rostedt
2018-05-01 15:27       ` Paul E. McKenney
2018-05-01  1:42 ` [PATCH RFC v5 4/6] trace/irqsoff: Split reset into seperate functions Joel Fernandes
2018-05-01  3:45   ` Randy Dunlap
2018-05-01  3:46     ` [kernel-team] " Joel Fernandes
2018-05-01  1:42 ` [PATCH RFC v5 5/6] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
2018-05-01  1:56   ` Joel Fernandes
2018-05-01 14:24     ` Steven Rostedt
2018-05-01 14:24   ` Steven Rostedt
2018-05-01 14:36     ` Paul E. McKenney
2018-05-01 15:16       ` Joel Fernandes
2018-05-01 15:21         ` Paul E. McKenney
2018-05-01 15:23           ` Joel Fernandes
2018-05-01 15:42             ` Paul E. McKenney
2018-05-01 15:53     ` Joel Fernandes
2018-05-01 16:44     ` Joel Fernandes [this message]
2018-05-01  1:42 ` [PATCH RFC v5 6/6] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes

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