From: Roland Dreier <rdreier@cisco.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@redhat.com>,
Martin Bligh <mbligh@google.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Mathieu Desnoyers <compudj@krystal.dyndns.org>,
Steven Rostedt <rostedt@goodmis.org>,
darren@dvhart.com, "Frank Ch. Eigler" <fche@redhat.com>,
systemtap-ml <systemtap@sources.redhat.com>
Subject: Re: Unified tracing buffer
Date: Mon, 22 Sep 2008 18:26:59 -0700 [thread overview]
Message-ID: <adaod2f649o.fsf@cisco.com> (raw)
In-Reply-To: <alpine.LFD.1.10.0809221718100.3265@nehalem.linux-foundation.org> (Linus Torvalds's message of "Mon, 22 Sep 2008 17:39:29 -0700 (PDT)")
> Because all it tells you is the ordering of the atomic increment, not of
> the caller. The atomic increment is not related to all the other ops that
> the code that you trace actually does in any shape or form, and so the
> ordering of the trace doesn't actually imply anything for the ordering of
> the operations you are tracing!
This reminds me of a naive question that occurred to me while we were
discussing this at KS. Namely, what does "ordering" mean for events?
An example I'm all too familiar with is the lack of ordering of MMIO on
big SGI systems -- if you forget an mmiowb(), then two CPUs taking a
spinlock and doing writel() inside the spinlock and then dropping the
spinlock (which should be enough to "order" things) might see the
writel() reach the final device "out of order" because the write has to
travel through a routed system fabric.
Just like Einstein said, it really seems to me that the order of things
depends on your frame of reference.
- R.
next prev parent reply other threads:[~2008-09-23 1:27 UTC|newest]
Thread overview: 122+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-19 21:33 Unified tracing buffer Martin Bligh
2008-09-19 21:42 ` Randy Dunlap
2008-09-19 21:57 ` Martin Bligh
2008-09-19 22:41 ` Olaf Dabrunz
2008-09-19 22:19 ` Martin Bligh
2008-09-20 8:10 ` Olaf Dabrunz
2008-09-20 8:29 ` Steven Rostedt
2008-09-20 11:40 ` Mathieu Desnoyers
2008-09-20 8:26 ` Steven Rostedt
2008-09-20 11:44 ` Mathieu Desnoyers
2008-09-19 22:28 ` Olaf Dabrunz
2008-09-19 22:09 ` Martin Bligh
2008-09-19 23:18 ` Frank Ch. Eigler
2008-09-20 8:50 ` Steven Rostedt
2008-09-20 13:37 ` Mathieu Desnoyers
2008-09-20 13:51 ` Steven Rostedt
2008-09-20 14:54 ` Steven Rostedt
2008-09-22 18:45 ` Mathieu Desnoyers
2008-09-22 21:39 ` Steven Rostedt
2008-09-23 3:27 ` Mathieu Desnoyers
2008-09-20 0:07 ` Peter Zijlstra
2008-09-22 14:07 ` K.Prasad
2008-09-22 14:45 ` Peter Zijlstra
2008-09-22 16:29 ` Martin Bligh
2008-09-22 16:36 ` Peter Zijlstra
2008-09-22 20:50 ` Masami Hiramatsu
2008-09-23 3:05 ` Mathieu Desnoyers
2008-09-23 2:49 ` Mathieu Desnoyers
2008-09-23 5:25 ` Tom Zanussi
2008-09-23 9:31 ` Peter Zijlstra
2008-09-23 18:13 ` Mathieu Desnoyers
2008-09-23 18:33 ` Christoph Lameter
2008-09-23 18:56 ` Linus Torvalds
2008-09-23 13:50 ` Mathieu Desnoyers
2008-09-23 14:00 ` Martin Bligh
2008-09-23 17:55 ` K.Prasad
2008-09-23 18:27 ` Martin Bligh
2008-09-24 3:50 ` Tom Zanussi
2008-09-24 5:42 ` K.Prasad
2008-09-25 6:07 ` [RFC PATCH 0/8] current relay cleanup patchset Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 1/8] relay - Clean up relay_switch_subbuf() and make waking up consumers optional Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 2/8] relay - Make the relay sub-buffer switch code replaceable Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 3/8] relay - Add channel flags to relay, remove global callback param Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 4/8] relay - Add reserved param to switch-subbuf, in preparation for non-pad write/reserve Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 5/8] relay - Map the first sub-buffer at the end of the buffer, for temporary convenience Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 6/8] relay - Replace relay_reserve/relay_write with non-padded versions Tom Zanussi
2008-09-25 6:07 ` [RFC PATCH 7/8] relay - Remove padding-related code from relay_read()/relay_splice_read() et al Tom Zanussi
2008-09-25 6:08 ` [RFC PATCH 8/8] relay - Clean up remaining padding-related junk Tom Zanussi
2008-09-23 5:27 ` [PATCH 1/3] relay - clean up subbuf switch Tom Zanussi
2008-09-23 20:15 ` Andrew Morton
2008-09-23 5:27 ` [PATCH 2/3] relay - make subbuf switch replaceable Tom Zanussi
2008-09-23 20:17 ` Andrew Morton
2008-09-23 5:27 ` [PATCH 3/3] relay - add channel flags Tom Zanussi
2008-09-23 20:20 ` Andrew Morton
2008-09-24 3:57 ` Tom Zanussi
2008-09-20 0:26 ` Unified tracing buffer Marcel Holtmann
2008-09-20 9:03 ` Steven Rostedt
2008-09-20 13:55 ` Mathieu Desnoyers
2008-09-20 14:12 ` Arjan van de Ven
2008-09-22 18:52 ` Mathieu Desnoyers
2008-10-02 15:28 ` Jason Baron
2008-10-03 16:11 ` Mathieu Desnoyers
2008-10-03 18:37 ` Jason Baron
2008-10-03 19:10 ` Mathieu Desnoyers
2008-10-03 19:25 ` Jason Baron
2008-10-03 19:56 ` Mathieu Desnoyers
2008-10-03 20:25 ` Jason Baron
2008-10-03 21:52 ` Frank Ch. Eigler
2008-09-22 3:09 ` KOSAKI Motohiro
2008-09-22 9:57 ` Peter Zijlstra
2008-09-23 2:36 ` Mathieu Desnoyers
2008-09-22 13:57 ` K.Prasad
2008-09-22 19:45 ` Masami Hiramatsu
2008-09-22 20:13 ` Martin Bligh
2008-09-22 22:25 ` Masami Hiramatsu
2008-09-22 23:11 ` Darren Hart
2008-09-23 0:04 ` Masami Hiramatsu
2008-09-22 23:16 ` Martin Bligh
2008-09-23 0:05 ` Masami Hiramatsu
2008-09-23 0:12 ` Martin Bligh
2008-09-23 14:49 ` Masami Hiramatsu
2008-09-23 15:04 ` Mathieu Desnoyers
2008-09-23 15:30 ` Masami Hiramatsu
2008-09-23 16:01 ` Linus Torvalds
2008-09-23 17:04 ` Masami Hiramatsu
2008-09-23 17:30 ` Thomas Gleixner
2008-09-23 18:59 ` Masami Hiramatsu
2008-09-23 19:36 ` Thomas Gleixner
2008-09-23 19:38 ` Martin Bligh
2008-09-23 19:41 ` Thomas Gleixner
2008-09-23 19:50 ` Martin Bligh
2008-09-23 20:03 ` Thomas Gleixner
2008-09-23 21:02 ` Martin Bligh
2008-09-23 20:03 ` Masami Hiramatsu
2008-09-23 20:08 ` Thomas Gleixner
2008-09-23 15:46 ` Linus Torvalds
2008-09-23 0:39 ` Linus Torvalds
2008-09-23 1:26 ` Roland Dreier [this message]
2008-09-23 1:39 ` Steven Rostedt
2008-09-23 2:02 ` Mathieu Desnoyers
2008-09-23 2:26 ` Darren Hart
2008-09-23 2:31 ` Mathieu Desnoyers
2008-09-23 3:26 ` Linus Torvalds
2008-09-23 3:36 ` Mathieu Desnoyers
2008-09-23 4:05 ` Linus Torvalds
2008-09-23 3:43 ` Steven Rostedt
2008-09-23 4:10 ` Masami Hiramatsu
2008-09-23 4:17 ` Martin Bligh
2008-09-23 15:23 ` Masami Hiramatsu
2008-09-23 10:53 ` Steven Rostedt
2008-09-23 4:19 ` Linus Torvalds
2008-09-23 14:12 ` Mathieu Desnoyers
2008-09-23 2:30 ` Mathieu Desnoyers
2008-09-23 3:06 ` Masami Hiramatsu
2008-09-23 14:36 ` KOSAKI Motohiro
2008-09-23 15:02 ` Frank Ch. Eigler
2008-09-23 15:21 ` Masami Hiramatsu
2008-09-23 17:59 ` KOSAKI Motohiro
2008-09-23 18:28 ` Martin Bligh
2008-09-23 3:33 ` Andi Kleen
2008-09-23 3:47 ` Martin Bligh
2008-09-23 5:04 ` Andi Kleen
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