From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Joel Fernandes <joelaf@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
LKML <linux-kernel@vger.kernel.org>,
"Cc: Android Kernel" <kernel-team@android.com>,
Boqun Feng <boqun.feng@gmail.com>,
Byungchul Park <byungchul.park@lge.com>,
Ingo Molnar <mingo@redhat.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Namhyung Kim <namhyung@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Glexiner <tglx@linutronix.de>,
Tom Zanussi <tom.zanussi@linux.intel.com>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage
Date: Wed, 8 Aug 2018 10:27:00 -0400 [thread overview]
Message-ID: <20180808102700.38c4169d@gandalf.local.home> (raw)
In-Reply-To: <20180808130041.GI24813@linux.vnet.ibm.com>
On Wed, 8 Aug 2018 06:00:41 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> I suppose that an srcu_read_lock_nmi() and srcu_read_unlock_nmi() could
> be added, which would do atomic ops on sp->sda->srcu_lock_count. Not sure
> whether this would be fast enough to be useful, but easy to provide:
>
> int __srcu_read_lock_nmi(struct srcu_struct *sp) /* UNTESTED. */
> {
> int idx;
>
> idx = READ_ONCE(sp->srcu_idx) & 0x1;
> atomic_inc(&sp->sda->srcu_lock_count[idx]);
> smp_mb__after_atomic(); /* B */ /* Avoid leaking critical section. */
> return idx;
> }
>
> void __srcu_read_unlock_nmi(struct srcu_struct *sp, int idx)
> {
> smp_mb__before_atomic(); /* C */ /* Avoid leaking critical section. */
> atomic_inc(&sp->sda->srcu_unlock_count[idx]);
> }
>
> With appropriate adjustments to also allow Tiny RCU to also work.
>
> Note that you have to use _nmi() everywhere, not just in NMI handlers.
> In fact, the NMI handlers are the one place you -don't- need to use
> _nmi(), strangely enough.
>
> Might be worth a try -- smp_mb__{before,after}_atomic() is a no-op on
> some architectures, for example.
Note this would kill the performance that srcu gives that Joel wants.
Switching from a this_cpu_inc() to a atomic_inc() would be a huge
impact.
There's also a local_inc() if you are using per cpu pointers, that is
suppose to guarantee atomicity for single cpu operations. That's what
the ftrace ring buffer uses.
-- Steve
next prev parent reply other threads:[~2018-08-08 14:27 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-30 22:24 [PATCH v12 0/3] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
2018-07-30 22:24 ` [PATCH v12 1/3] lockdep: use this_cpu_ptr instead of get_cpu_var stats Joel Fernandes
2018-07-30 22:24 ` [PATCH v12 2/3] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
2018-07-30 23:10 ` Steven Rostedt
2018-08-10 15:35 ` Steven Rostedt
2018-08-10 16:32 ` Steven Rostedt
2018-07-30 22:24 ` [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
2018-08-06 19:50 ` Steven Rostedt
2018-08-07 0:43 ` Joel Fernandes
2018-08-07 1:43 ` Steven Rostedt
2018-08-07 13:33 ` Joel Fernandes
2018-08-07 13:49 ` Steven Rostedt
2018-08-07 14:10 ` Joel Fernandes
2018-08-07 14:34 ` Steven Rostedt
2018-08-07 14:48 ` Joel Fernandes
2018-08-07 15:09 ` Steven Rostedt
2018-08-07 15:24 ` Joel Fernandes
2018-08-07 23:45 ` Steven Rostedt
2018-08-07 23:54 ` Joel Fernandes
2018-08-08 0:48 ` Steven Rostedt
2018-08-08 1:17 ` Joel Fernandes
2018-08-08 1:55 ` Steven Rostedt
2018-08-08 2:13 ` Joel Fernandes
2018-08-08 2:28 ` Steven Rostedt
2018-08-08 3:44 ` Joel Fernandes
2018-08-08 3:53 ` Joel Fernandes
2018-08-08 5:06 ` Joel Fernandes
2018-08-08 12:46 ` Steven Rostedt
2018-08-08 13:03 ` Paul E. McKenney
2018-08-08 13:07 ` Steven Rostedt
2018-08-08 14:33 ` Paul E. McKenney
2018-08-08 14:49 ` Steven Rostedt
2018-08-08 15:05 ` Paul E. McKenney
2018-08-08 15:23 ` Steven Rostedt
2018-08-08 16:02 ` Paul E. McKenney
2018-08-08 16:24 ` Steven Rostedt
2018-08-08 17:21 ` Paul E. McKenney
2018-08-08 13:00 ` Paul E. McKenney
2018-08-08 14:10 ` Joel Fernandes
2018-08-08 14:49 ` Paul E. McKenney
2018-08-08 19:24 ` Joel Fernandes
2018-08-08 20:18 ` Paul E. McKenney
2018-08-08 22:15 ` Joel Fernandes
2018-08-08 22:47 ` Paul E. McKenney
2018-08-09 12:18 ` joel
2018-08-08 14:27 ` Steven Rostedt [this message]
2018-08-08 14:42 ` Paul E. McKenney
2018-08-08 15:27 ` Steven Rostedt
2018-08-08 16:03 ` Paul E. McKenney
2018-08-02 14:55 ` [PATCH v12 0/3] " Masami Hiramatsu
2018-08-03 2:57 ` Joel Fernandes
2018-08-03 7:23 ` Masami Hiramatsu
2018-08-04 4:51 ` Joel Fernandes
2018-08-05 16:46 ` Joel Fernandes
2018-08-06 2:07 ` Masami Hiramatsu
2018-08-06 15:24 ` Joel Fernandes
2018-08-03 7:34 ` Masami Hiramatsu
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