From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
Waiman Long <waiman.long@hp.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>,
Michel Lespinasse <walken@google.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
Matthew R Wilcox <matthew.r.wilcox@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Rik van Riel <riel@redhat.com>,
Peter Hurley <peter@hurleysoftware.com>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
George Spelvin <linux@horizon.com>
Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections
Date: Mon, 25 Nov 2013 13:09:02 +0100 [thread overview]
Message-ID: <20131125120902.GY10022@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFzr7=N=_t03Luzxg2Ln9_h+M9Ud5spLi7FH+5j7ynkPUg@mail.gmail.com>
On Sat, Nov 23, 2013 at 12:39:53PM -0800, Linus Torvalds wrote:
> On Sat, Nov 23, 2013 at 12:21 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > And as far as I can tell, the above gives you: A < B < C < D < E < F <
> > A. Which doesn't look possible.
>
> Hmm.. I guess technically all of those cases aren't "strictly
> precedes" as much as "cannot have happened in the opposite order". So
> the "<" might be "<=". Which I guess *is* possible: "it all happened
> at the same time". And then the difference between your suggested
> "lwsync" and "sync" in the unlock path on CPU0 basically approximating
> the difference between "A <= B" and "A < B"..
>
> Ho humm.
But remember, there's an actual full proper barrier between E and F, so
at best you'd end up with something like:
A <= B <= C <= D <= E < F <= A
Which is still an impossibility.
I'm hoping others will explain things, as I'm very much on shaky ground
myself wrt transitivity.
--
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
Waiman Long <waiman.long@hp.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>,
Michel Lespinasse <walken@google.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
Matthew R Wilcox <matthew.r.wilcox@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Rik van Riel <riel@redhat.com>,
Peter Hurley <peter@hurleysoftware.com>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
George Spelvin <linux@horizon.com>,
"H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
Aswin Chandramouleeswaran <aswin@hp.com>,
Scott J Norton <scott.norton@hp.com>,
"Figo.zhang" <figo1802@gmail.com>
Subject: Re: [PATCH v6 4/5] MCS Lock: Barrier corrections
Date: Mon, 25 Nov 2013 13:09:02 +0100 [thread overview]
Message-ID: <20131125120902.GY10022@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFzr7=N=_t03Luzxg2Ln9_h+M9Ud5spLi7FH+5j7ynkPUg@mail.gmail.com>
On Sat, Nov 23, 2013 at 12:39:53PM -0800, Linus Torvalds wrote:
> On Sat, Nov 23, 2013 at 12:21 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > And as far as I can tell, the above gives you: A < B < C < D < E < F <
> > A. Which doesn't look possible.
>
> Hmm.. I guess technically all of those cases aren't "strictly
> precedes" as much as "cannot have happened in the opposite order". So
> the "<" might be "<=". Which I guess *is* possible: "it all happened
> at the same time". And then the difference between your suggested
> "lwsync" and "sync" in the unlock path on CPU0 basically approximating
> the difference between "A <= B" and "A < B"..
>
> Ho humm.
But remember, there's an actual full proper barrier between E and F, so
at best you'd end up with something like:
A <= B <= C <= D <= E < F <= A
Which is still an impossibility.
I'm hoping others will explain things, as I'm very much on shaky ground
myself wrt transitivity.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2013-11-25 12:09 UTC|newest]
Thread overview: 239+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1384885312.git.tim.c.chen@linux.intel.com>
2013-11-20 1:37 ` [PATCH v6 0/5] MCS Lock: MCS lock code cleanup and optimizations Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 10:19 ` Will Deacon
2013-11-20 10:19 ` Will Deacon
2013-11-20 12:50 ` Paul E. McKenney
2013-11-20 12:50 ` Paul E. McKenney
2013-11-20 17:00 ` Will Deacon
2013-11-20 17:00 ` Will Deacon
2013-11-20 17:14 ` Paul E. McKenney
2013-11-20 17:14 ` Paul E. McKenney
2013-11-20 17:00 ` Tim Chen
2013-11-20 17:00 ` Tim Chen
2013-11-20 17:16 ` Paul E. McKenney
2013-11-20 17:16 ` Paul E. McKenney
2013-11-20 1:37 ` [PATCH v6 1/5] MCS Lock: Restructure the MCS lock defines and locking code into its own file Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` [PATCH v6 2/5] MCS Lock: optimizations and extra comments Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` [PATCH v6 3/5] MCS Lock: Move mcs_lock/unlock function into its own file Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` [PATCH v6 4/5] MCS Lock: Barrier corrections Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 15:31 ` Paul E. McKenney
2013-11-20 15:31 ` Paul E. McKenney
2013-11-20 15:31 ` Paul E. McKenney
2013-11-20 15:46 ` Will Deacon
2013-11-20 15:46 ` Will Deacon
2013-11-20 17:14 ` Paul E. McKenney
2013-11-20 17:14 ` Paul E. McKenney
2013-11-20 18:43 ` Tim Chen
2013-11-20 18:43 ` Tim Chen
2013-11-20 19:06 ` Paul E. McKenney
2013-11-20 19:06 ` Paul E. McKenney
2013-11-20 20:36 ` Tim Chen
2013-11-20 20:36 ` Tim Chen
2013-11-20 21:44 ` Paul E. McKenney
2013-11-20 21:44 ` Paul E. McKenney
2013-11-20 23:51 ` Tim Chen
2013-11-20 23:51 ` Tim Chen
2013-11-21 4:53 ` Paul E. McKenney
2013-11-21 4:53 ` Paul E. McKenney
2013-11-21 10:17 ` Will Deacon
2013-11-21 10:17 ` Will Deacon
2013-11-21 13:16 ` Paul E. McKenney
2013-11-21 13:16 ` Paul E. McKenney
2013-11-21 10:45 ` Peter Zijlstra
2013-11-21 10:45 ` Peter Zijlstra
2013-11-21 13:18 ` Paul E. McKenney
2013-11-21 13:18 ` Paul E. McKenney
2013-11-21 22:27 ` Linus Torvalds
2013-11-21 22:27 ` Linus Torvalds
2013-11-21 22:52 ` Paul E. McKenney
2013-11-21 22:52 ` Paul E. McKenney
2013-11-22 0:09 ` Linus Torvalds
2013-11-22 0:09 ` Linus Torvalds
2013-11-22 4:08 ` Paul E. McKenney
2013-11-22 4:08 ` Paul E. McKenney
2013-11-22 4:25 ` Linus Torvalds
2013-11-22 4:25 ` Linus Torvalds
2013-11-22 6:23 ` Paul E. McKenney
2013-11-22 6:23 ` Paul E. McKenney
2013-11-22 15:16 ` Ingo Molnar
2013-11-22 15:16 ` Ingo Molnar
2013-11-22 18:49 ` Paul E. McKenney
2013-11-22 18:49 ` Paul E. McKenney
2013-11-22 19:06 ` Linus Torvalds
2013-11-22 19:06 ` Linus Torvalds
2013-11-22 20:06 ` Paul E. McKenney
2013-11-22 20:06 ` Paul E. McKenney
2013-11-22 20:09 ` Linus Torvalds
2013-11-22 20:09 ` Linus Torvalds
2013-11-22 20:37 ` Paul E. McKenney
2013-11-22 20:37 ` Paul E. McKenney
2013-11-22 21:01 ` Linus Torvalds
2013-11-22 21:01 ` Linus Torvalds
2013-11-22 21:52 ` Paul E. McKenney
2013-11-22 21:52 ` Paul E. McKenney
2013-11-22 22:19 ` Linus Torvalds
2013-11-22 22:19 ` Linus Torvalds
2013-11-23 0:25 ` Paul E. McKenney
2013-11-23 0:25 ` Paul E. McKenney
2013-11-23 0:42 ` Linus Torvalds
2013-11-23 0:42 ` Linus Torvalds
2013-11-23 1:36 ` Paul E. McKenney
2013-11-23 1:36 ` Paul E. McKenney
2013-11-23 2:11 ` Linus Torvalds
2013-11-23 2:11 ` Linus Torvalds
2013-11-23 4:05 ` Paul E. McKenney
2013-11-23 4:05 ` Paul E. McKenney
2013-11-23 11:24 ` Ingo Molnar
2013-11-23 11:24 ` Ingo Molnar
2013-11-23 17:06 ` Paul E. McKenney
2013-11-23 17:06 ` Paul E. McKenney
2013-11-26 12:02 ` Ingo Molnar
2013-11-26 12:02 ` Ingo Molnar
2013-11-26 19:28 ` Paul E. McKenney
2013-11-26 19:28 ` Paul E. McKenney
2013-11-23 20:21 ` Linus Torvalds
2013-11-23 20:21 ` Linus Torvalds
2013-11-23 20:39 ` Linus Torvalds
2013-11-23 20:39 ` Linus Torvalds
2013-11-25 12:09 ` Peter Zijlstra [this message]
2013-11-25 12:09 ` Peter Zijlstra
2013-11-25 17:18 ` Will Deacon
2013-11-25 17:18 ` Will Deacon
2013-11-25 17:56 ` Paul E. McKenney
2013-11-25 17:56 ` Paul E. McKenney
2013-11-25 17:54 ` Paul E. McKenney
2013-11-25 17:54 ` Paul E. McKenney
2013-11-23 21:29 ` Peter Zijlstra
2013-11-23 21:29 ` Peter Zijlstra
2013-11-23 22:24 ` Linus Torvalds
2013-11-23 22:24 ` Linus Torvalds
2013-11-25 17:53 ` Paul E. McKenney
2013-11-25 17:53 ` Paul E. McKenney
2013-11-25 18:21 ` Peter Zijlstra
2013-11-25 18:21 ` Peter Zijlstra
2013-11-21 11:03 ` Peter Zijlstra
2013-11-21 11:03 ` Peter Zijlstra
2013-11-21 12:56 ` Peter Zijlstra
2013-11-21 12:56 ` Peter Zijlstra
2013-11-21 13:20 ` Paul E. McKenney
2013-11-21 13:20 ` Paul E. McKenney
2013-11-21 17:25 ` Paul E. McKenney
2013-11-21 17:25 ` Paul E. McKenney
2013-11-21 21:52 ` Peter Zijlstra
2013-11-21 21:52 ` Peter Zijlstra
2013-11-21 22:18 ` Paul E. McKenney
2013-11-21 22:18 ` Paul E. McKenney
2013-11-22 15:58 ` Peter Zijlstra
2013-11-22 15:58 ` Peter Zijlstra
2013-11-22 18:26 ` Paul E. McKenney
2013-11-22 18:26 ` Paul E. McKenney
2013-11-22 18:51 ` Peter Zijlstra
2013-11-22 18:51 ` Peter Zijlstra
2013-11-22 18:59 ` Paul E. McKenney
2013-11-22 18:59 ` Paul E. McKenney
2013-11-25 17:35 ` Peter Zijlstra
2013-11-25 17:35 ` Peter Zijlstra
2013-11-25 18:02 ` Paul E. McKenney
2013-11-25 18:02 ` Paul E. McKenney
2013-11-25 18:24 ` Peter Zijlstra
2013-11-25 18:24 ` Peter Zijlstra
2013-11-25 18:34 ` Tim Chen
2013-11-25 18:34 ` Tim Chen
2013-11-25 18:27 ` Peter Zijlstra
2013-11-25 18:27 ` Peter Zijlstra
2013-11-25 23:52 ` Paul E. McKenney
2013-11-25 23:52 ` Paul E. McKenney
2013-11-26 9:59 ` Peter Zijlstra
2013-11-26 9:59 ` Peter Zijlstra
2013-11-26 17:11 ` Paul E. McKenney
2013-11-26 17:11 ` Paul E. McKenney
2013-11-26 17:18 ` Peter Zijlstra
2013-11-26 17:18 ` Peter Zijlstra
2013-11-26 19:00 ` Linus Torvalds
2013-11-26 19:00 ` Linus Torvalds
2013-11-26 19:20 ` Paul E. McKenney
2013-11-26 19:20 ` Paul E. McKenney
2013-11-26 19:32 ` Linus Torvalds
2013-11-26 19:32 ` Linus Torvalds
2013-11-26 22:51 ` Paul E. McKenney
2013-11-26 22:51 ` Paul E. McKenney
2013-11-26 23:58 ` Linus Torvalds
2013-11-26 23:58 ` Linus Torvalds
2013-11-27 0:21 ` Thomas Gleixner
2013-11-27 0:21 ` Thomas Gleixner
2013-11-27 0:39 ` Paul E. McKenney
2013-11-27 0:39 ` Paul E. McKenney
2013-11-27 1:05 ` Linus Torvalds
2013-11-27 1:05 ` Linus Torvalds
2013-11-27 1:31 ` Paul E. McKenney
2013-11-27 1:31 ` Paul E. McKenney
2013-11-27 10:16 ` Will Deacon
2013-11-27 10:16 ` Will Deacon
2013-11-27 17:11 ` Paul E. McKenney
2013-11-27 17:11 ` Paul E. McKenney
2013-11-28 11:40 ` Will Deacon
2013-11-28 11:40 ` Will Deacon
2013-11-28 17:38 ` Paul E. McKenney
2013-11-28 17:38 ` Paul E. McKenney
2013-11-28 18:03 ` Will Deacon
2013-11-28 18:03 ` Will Deacon
2013-11-28 18:27 ` Paul E. McKenney
2013-11-28 18:27 ` Paul E. McKenney
2013-11-28 18:53 ` Will Deacon
2013-11-28 18:53 ` Will Deacon
2013-11-28 19:50 ` Paul E. McKenney
2013-11-28 19:50 ` Paul E. McKenney
2013-11-29 16:17 ` Will Deacon
2013-11-29 16:17 ` Will Deacon
2013-11-29 16:44 ` Linus Torvalds
2013-11-29 16:44 ` Linus Torvalds
2013-11-29 18:18 ` Will Deacon
2013-11-29 18:18 ` Will Deacon
2013-11-30 17:38 ` Paul E. McKenney
2013-11-30 17:38 ` Paul E. McKenney
2013-11-26 19:21 ` Peter Zijlstra
2013-11-26 19:21 ` Peter Zijlstra
2013-11-27 16:58 ` Oleg Nesterov
2013-11-27 16:58 ` Oleg Nesterov
2013-11-26 23:08 ` Benjamin Herrenschmidt
2013-11-26 23:08 ` Benjamin Herrenschmidt
2013-11-25 23:55 ` H. Peter Anvin
2013-11-25 23:55 ` H. Peter Anvin
2013-11-26 3:16 ` Paul E. McKenney
2013-11-26 3:16 ` Paul E. McKenney
2013-11-27 0:46 ` H. Peter Anvin
2013-11-27 0:46 ` H. Peter Anvin
2013-11-27 1:07 ` Linus Torvalds
2013-11-27 1:07 ` Linus Torvalds
2013-11-27 1:27 ` Paul E. McKenney
2013-11-27 1:27 ` Paul E. McKenney
2013-11-27 2:59 ` H. Peter Anvin
2013-11-27 2:59 ` H. Peter Anvin
2013-11-25 18:52 ` H. Peter Anvin
2013-11-25 18:52 ` H. Peter Anvin
2013-11-25 22:58 ` Tim Chen
2013-11-25 22:58 ` Tim Chen
2013-11-25 23:28 ` H. Peter Anvin
2013-11-25 23:28 ` H. Peter Anvin
2013-11-25 23:51 ` Paul E. McKenney
2013-11-25 23:51 ` Paul E. McKenney
2013-11-25 23:36 ` Paul E. McKenney
2013-11-25 23:36 ` Paul E. McKenney
2013-12-04 21:26 ` Andi Kleen
2013-12-04 21:26 ` Andi Kleen
2013-12-04 22:07 ` Paul E. McKenney
2013-12-04 22:07 ` Paul E. McKenney
2013-11-21 13:19 ` Paul E. McKenney
2013-11-21 13:19 ` Paul E. McKenney
2013-11-20 1:37 ` [PATCH v6 5/5] MCS Lock: Allows for architecture specific mcs lock and unlock Tim Chen
2013-11-20 1:37 ` Tim Chen
2013-11-20 1:37 ` Tim Chen
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