From: Victor Kaplansky <VICTORK@il.ibm.com>
To: "David Laight" <David.Laight@aculab.com>
Cc: "Anton Blanchard" <anton@samba.org>,
"Frederic Weisbecker" <fweisbec@gmail.com>,
"LKML" <linux-kernel@vger.kernel.org>,
"Linux PPC dev" <linuxppc-dev@ozlabs.org>,
"Mathieu Desnoyers" <mathieu.desnoyers@polymtl.ca>,
"Michael Neuling" <mikey@neuling.org>,
"Oleg Nesterov" <oleg@redhat.com>,
paulmck@linux.vnet.ibm.com,
"Peter Zijlstra" <peterz@infradead.org>
Subject: RE: perf events ring buffer memory barrier on powerpc
Date: Thu, 31 Oct 2013 14:55:25 +0200 [thread overview]
Message-ID: <OFF094B66E.899BE5FF-ON42257C15.0045F3A1-42257C15.0046FE15@il.ibm.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B73CC@saturn3.aculab.com>
"David Laight" <David.Laight@aculab.com> wrote on 10/31/2013 02:28:56 PM:
> So even though the wmb() in the writer ensures the writes are correctly
> ordered, the reader can read the old value from the second location from
> its local cache.
In case of circular buffer, the only thing that producer reads is @tail,
and nothing wrong will happen if producer reads old value of @tail.
Moreover,
adherents of smp_mb() insert it *after* the read of @tail, so it cannot
prevent reading of old value anyway.
-- Victor
WARNING: multiple messages have this Message-ID (diff)
From: Victor Kaplansky <VICTORK@il.ibm.com>
To: "David Laight" <David.Laight@aculab.com>
Cc: Michael Neuling <mikey@neuling.org>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Oleg Nesterov <oleg@redhat.com>,
Linux PPC dev <linuxppc-dev@ozlabs.org>,
Anton Blanchard <anton@samba.org>,
paulmck@linux.vnet.ibm.com
Subject: RE: perf events ring buffer memory barrier on powerpc
Date: Thu, 31 Oct 2013 14:55:25 +0200 [thread overview]
Message-ID: <OFF094B66E.899BE5FF-ON42257C15.0045F3A1-42257C15.0046FE15@il.ibm.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B73CC@saturn3.aculab.com>
"David Laight" <David.Laight@aculab.com> wrote on 10/31/2013 02:28:56 PM:
> So even though the wmb() in the writer ensures the writes are correctly
> ordered, the reader can read the old value from the second location from
> its local cache.
In case of circular buffer, the only thing that producer reads is @tail,
and nothing wrong will happen if producer reads old value of @tail.
Moreover,
adherents of smp_mb() insert it *after* the read of @tail, so it cannot
prevent reading of old value anyway.
-- Victor
next prev parent reply other threads:[~2013-10-31 12:56 UTC|newest]
Thread overview: 215+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-22 23:54 perf events ring buffer memory barrier on powerpc Michael Neuling
2013-10-23 7:39 ` Victor Kaplansky
2013-10-23 7:39 ` Victor Kaplansky
2013-10-23 14:19 ` Frederic Weisbecker
2013-10-23 14:19 ` Frederic Weisbecker
2013-10-23 14:25 ` Frederic Weisbecker
2013-10-23 14:25 ` Frederic Weisbecker
2013-10-25 17:37 ` Peter Zijlstra
2013-10-25 17:37 ` Peter Zijlstra
2013-10-25 20:31 ` Michael Neuling
2013-10-25 20:31 ` Michael Neuling
2013-10-27 9:00 ` Victor Kaplansky
2013-10-27 9:00 ` Victor Kaplansky
2013-10-28 9:22 ` Peter Zijlstra
2013-10-28 9:22 ` Peter Zijlstra
2013-10-28 10:02 ` Frederic Weisbecker
2013-10-28 10:02 ` Frederic Weisbecker
2013-10-28 12:38 ` Victor Kaplansky
2013-10-28 12:38 ` Victor Kaplansky
2013-10-28 13:26 ` Peter Zijlstra
2013-10-28 13:26 ` Peter Zijlstra
2013-10-28 16:34 ` Paul E. McKenney
2013-10-28 16:34 ` Paul E. McKenney
2013-10-28 20:17 ` Oleg Nesterov
2013-10-28 20:17 ` Oleg Nesterov
2013-10-28 20:58 ` Victor Kaplansky
2013-10-28 20:58 ` Victor Kaplansky
2013-10-29 10:21 ` Peter Zijlstra
2013-10-29 10:21 ` Peter Zijlstra
2013-10-29 10:30 ` Peter Zijlstra
2013-10-29 10:30 ` Peter Zijlstra
2013-10-29 10:35 ` Peter Zijlstra
2013-10-29 10:35 ` Peter Zijlstra
2013-10-29 20:15 ` Oleg Nesterov
2013-10-29 20:15 ` Oleg Nesterov
2013-10-29 19:27 ` Vince Weaver
2013-10-29 19:27 ` Vince Weaver
2013-10-30 10:42 ` Peter Zijlstra
2013-10-30 10:42 ` Peter Zijlstra
2013-10-30 11:48 ` James Hogan
2013-10-30 11:48 ` James Hogan
2013-10-30 12:48 ` Peter Zijlstra
2013-10-30 12:48 ` Peter Zijlstra
2013-11-06 13:19 ` [tip:perf/core] tools/perf: Add required memory barriers tip-bot for Peter Zijlstra
2013-11-06 13:50 ` Vince Weaver
2013-11-06 14:00 ` Peter Zijlstra
2013-11-06 14:28 ` Peter Zijlstra
2013-11-06 14:55 ` Vince Weaver
2013-11-06 15:10 ` Peter Zijlstra
2013-11-06 15:23 ` Peter Zijlstra
2013-11-06 14:44 ` Peter Zijlstra
2013-11-06 16:07 ` Peter Zijlstra
2013-11-06 17:31 ` Vince Weaver
2013-11-06 18:24 ` Peter Zijlstra
2013-11-07 8:21 ` Ingo Molnar
2013-11-07 14:27 ` Vince Weaver
2013-11-07 15:55 ` Ingo Molnar
2013-11-11 16:24 ` Peter Zijlstra
2013-11-11 21:10 ` Ingo Molnar
2013-10-29 21:23 ` perf events ring buffer memory barrier on powerpc Michael Neuling
2013-10-29 21:23 ` Michael Neuling
2013-10-30 9:27 ` Paul E. McKenney
2013-10-30 9:27 ` Paul E. McKenney
2013-10-30 11:25 ` Peter Zijlstra
2013-10-30 11:25 ` Peter Zijlstra
2013-10-30 14:52 ` Victor Kaplansky
2013-10-30 14:52 ` Victor Kaplansky
2013-10-30 15:39 ` Peter Zijlstra
2013-10-30 15:39 ` Peter Zijlstra
2013-10-30 17:14 ` Victor Kaplansky
2013-10-30 17:14 ` Victor Kaplansky
2013-10-30 17:44 ` Peter Zijlstra
2013-10-30 17:44 ` Peter Zijlstra
2013-10-31 6:16 ` Paul E. McKenney
2013-10-31 6:16 ` Paul E. McKenney
2013-11-01 13:12 ` Victor Kaplansky
2013-11-01 13:12 ` Victor Kaplansky
2013-11-02 16:36 ` Paul E. McKenney
2013-11-02 16:36 ` Paul E. McKenney
2013-11-02 17:26 ` Paul E. McKenney
2013-11-02 17:26 ` Paul E. McKenney
2013-10-31 6:40 ` Paul E. McKenney
2013-10-31 6:40 ` Paul E. McKenney
2013-11-01 14:25 ` Victor Kaplansky
2013-11-01 14:25 ` Victor Kaplansky
2013-11-02 17:28 ` Paul E. McKenney
2013-11-02 17:28 ` Paul E. McKenney
2013-11-01 14:56 ` Peter Zijlstra
2013-11-01 14:56 ` Peter Zijlstra
2013-11-02 17:32 ` Paul E. McKenney
2013-11-02 17:32 ` Paul E. McKenney
2013-11-03 14:40 ` Paul E. McKenney
2013-11-03 14:40 ` Paul E. McKenney
2013-11-03 15:17 ` [RFC] arch: Introduce new TSO memory barrier smp_tmb() Peter Zijlstra
2013-11-03 15:17 ` Peter Zijlstra
2013-11-03 18:08 ` Linus Torvalds
2013-11-03 18:08 ` Linus Torvalds
2013-11-03 20:01 ` Peter Zijlstra
2013-11-03 20:01 ` Peter Zijlstra
2013-11-03 22:42 ` Paul E. McKenney
2013-11-03 22:42 ` Paul E. McKenney
2013-11-03 23:34 ` Linus Torvalds
2013-11-03 23:34 ` Linus Torvalds
2013-11-04 10:51 ` Paul E. McKenney
2013-11-04 10:51 ` Paul E. McKenney
2013-11-04 11:22 ` Peter Zijlstra
2013-11-04 11:22 ` Peter Zijlstra
2013-11-04 16:27 ` Paul E. McKenney
2013-11-04 16:27 ` Paul E. McKenney
2013-11-04 16:48 ` Peter Zijlstra
2013-11-04 16:48 ` Peter Zijlstra
2013-11-04 19:11 ` Peter Zijlstra
2013-11-04 19:11 ` Peter Zijlstra
2013-11-04 19:18 ` Peter Zijlstra
2013-11-04 19:18 ` Peter Zijlstra
2013-11-04 20:54 ` Paul E. McKenney
2013-11-04 20:54 ` Paul E. McKenney
2013-11-04 20:53 ` Paul E. McKenney
2013-11-04 20:53 ` Paul E. McKenney
2013-11-05 14:05 ` Will Deacon
2013-11-05 14:05 ` Will Deacon
2013-11-05 14:49 ` Paul E. McKenney
2013-11-05 14:49 ` Paul E. McKenney
2013-11-05 18:49 ` Peter Zijlstra
2013-11-05 18:49 ` Peter Zijlstra
2013-11-06 11:00 ` Will Deacon
2013-11-06 11:00 ` Will Deacon
2013-11-06 12:39 ` Peter Zijlstra
2013-11-06 12:39 ` Peter Zijlstra
2013-11-06 12:51 ` Geert Uytterhoeven
2013-11-06 12:51 ` Geert Uytterhoeven
2013-11-06 13:57 ` Peter Zijlstra
2013-11-06 13:57 ` Peter Zijlstra
2013-11-06 18:48 ` Paul E. McKenney
2013-11-06 18:48 ` Paul E. McKenney
2013-11-06 19:42 ` Peter Zijlstra
2013-11-06 19:42 ` Peter Zijlstra
2013-11-07 11:17 ` Will Deacon
2013-11-07 11:17 ` Will Deacon
2013-11-07 13:36 ` Peter Zijlstra
2013-11-07 13:36 ` Peter Zijlstra
2013-11-07 23:50 ` Mathieu Desnoyers
2013-11-07 23:50 ` Mathieu Desnoyers
2013-11-04 11:05 ` Will Deacon
2013-11-04 11:05 ` Will Deacon
2013-11-04 16:34 ` Paul E. McKenney
2013-11-04 16:34 ` Paul E. McKenney
2013-11-03 20:59 ` Benjamin Herrenschmidt
2013-11-03 20:59 ` Benjamin Herrenschmidt
2013-11-03 22:43 ` Paul E. McKenney
2013-11-03 22:43 ` Paul E. McKenney
2013-11-03 17:07 ` perf events ring buffer memory barrier on powerpc Will Deacon
2013-11-03 22:47 ` Paul E. McKenney
2013-11-04 9:57 ` Will Deacon
2013-11-04 10:52 ` Paul E. McKenney
2013-11-01 16:11 ` Peter Zijlstra
2013-11-01 16:11 ` Peter Zijlstra
2013-11-02 17:46 ` Paul E. McKenney
2013-11-02 17:46 ` Paul E. McKenney
2013-11-01 16:18 ` Peter Zijlstra
2013-11-01 16:18 ` Peter Zijlstra
2013-11-02 17:49 ` Paul E. McKenney
2013-11-02 17:49 ` Paul E. McKenney
2013-10-30 13:28 ` Victor Kaplansky
2013-10-30 13:28 ` Victor Kaplansky
2013-10-30 15:51 ` Peter Zijlstra
2013-10-30 15:51 ` Peter Zijlstra
2013-10-30 18:29 ` Peter Zijlstra
2013-10-30 18:29 ` Peter Zijlstra
2013-10-30 19:11 ` Peter Zijlstra
2013-10-30 19:11 ` Peter Zijlstra
2013-10-31 4:33 ` Paul E. McKenney
2013-10-31 4:33 ` Paul E. McKenney
2013-10-31 4:32 ` Paul E. McKenney
2013-10-31 4:32 ` Paul E. McKenney
2013-10-31 9:04 ` Peter Zijlstra
2013-10-31 9:04 ` Peter Zijlstra
2013-10-31 15:07 ` Paul E. McKenney
2013-10-31 15:07 ` Paul E. McKenney
2013-10-31 15:19 ` Peter Zijlstra
2013-10-31 15:19 ` Peter Zijlstra
2013-11-01 9:28 ` Paul E. McKenney
2013-11-01 9:28 ` Paul E. McKenney
2013-11-01 10:30 ` Peter Zijlstra
2013-11-01 10:30 ` Peter Zijlstra
2013-11-02 15:20 ` Paul E. McKenney
2013-11-02 15:20 ` Paul E. McKenney
2013-11-04 9:07 ` Peter Zijlstra
2013-11-04 9:07 ` Peter Zijlstra
2013-11-04 10:00 ` Paul E. McKenney
2013-11-04 10:00 ` Paul E. McKenney
2013-10-31 9:59 ` Victor Kaplansky
2013-10-31 9:59 ` Victor Kaplansky
2013-10-31 12:28 ` David Laight
2013-10-31 12:28 ` David Laight
2013-10-31 12:55 ` Victor Kaplansky [this message]
2013-10-31 12:55 ` Victor Kaplansky
2013-10-31 15:25 ` Paul E. McKenney
2013-10-31 15:25 ` Paul E. McKenney
2013-11-01 16:06 ` Victor Kaplansky
2013-11-01 16:06 ` Victor Kaplansky
2013-11-01 16:25 ` David Laight
2013-11-01 16:25 ` David Laight
2013-11-01 16:30 ` Victor Kaplansky
2013-11-01 16:30 ` Victor Kaplansky
2013-11-03 20:57 ` Benjamin Herrenschmidt
2013-11-03 20:57 ` Benjamin Herrenschmidt
2013-11-02 15:46 ` Paul E. McKenney
2013-11-02 15:46 ` Paul E. McKenney
2013-10-28 19:09 ` Oleg Nesterov
2013-10-28 19:09 ` Oleg Nesterov
2013-10-29 14:06 ` [tip:perf/urgent] perf: Fix perf ring buffer memory ordering tip-bot for Peter Zijlstra
2014-05-08 20:46 perf events ring buffer memory barrier on powerpc Mikulas Patocka
[not found] ` <OF667059AA.7F151BCC-ONC2257CD3.0036CFEB-C2257CD3.003BBF01@il.ibm.com>
2014-05-09 12:20 ` Mikulas Patocka
2014-05-09 13:47 ` Paul E. McKenney
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