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From: Joel Fernandes <joelaf@google.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.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>,
	Fenguang Wu <fengguang.wu@intel.com>,
	Baohong Liu <baohong.liu@intel.com>,
	Vedang Patel <vedang.patel@intel.com>
Subject: Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
Date: Tue, 01 May 2018 01:18:09 +0000	[thread overview]
Message-ID: <CAJWu+ooJLUJZ5nArFPbxsoRy6Rbp4ipR3njdZUXSPT0Ng1yy6A@mail.gmail.com> (raw)
In-Reply-To: <20180418180250.7b6038dddba46b37c94b796c@kernel.org>

On Wed, Apr 18, 2018 at 2:02 AM Masami Hiramatsu <mhiramat@kernel.org>
wrote:

> On Mon, 16 Apr 2018 21:07:47 -0700
> Joel Fernandes <joelaf@google.com> wrote:

> > With TRACE_IRQFLAGS, we call trace_ API too many times. We don't need
> > to if local_irq_restore or local_irq_save didn't actually do anything.
> >
> > This gives around a 4% improvement in performance when doing the
> > following command: "time find / > /dev/null"
> >
> > Also its best to avoid these calls where possible, since in this series,
> > the RCU code in tracepoint.h seems to be call these quite a bit and I'd
> > like to keep this overhead low.

> Can we assume that the "flags" has only 1 bit irq-disable flag?
> Since it skips calling raw_local_irq_restore(flags); too,
> if there is any state in the flags on any arch, it may change the
> result. In that case, we can do it as below (just skipping
trace_hardirqs_*)

> int disabled = irqs_disabled();

> if (!raw_irqs_disabled_flags(flags) && disabled)
>          trace_hardirqs_on();

> raw_local_irq_restore(flags);

> if (raw_irqs_disabled_flags(flags) && !disabled)
>          trace_hardirqs_off();

With changes to the tracepoint implementation which uses srcu instead of
rcu, I'm not able to see a performance improvement with the above patch.
For this reason, I will drop this patch from next series. thanks,

- Joel

  parent reply	other threads:[~2018-05-01  1:18 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
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 [this message]
2018-04-17  4:07 ` [RFC v4 4/4] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes

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