From: Nick Piggin <piggin@cyberone•com.au>
To: Satyam Sharma <satyam@infradead•org>
Cc: Stefan Richter <stefanr@s5r6•in-berlin.de>,
paulmck@linux•vnet.ibm.com,
Herbert Xu <herbert@gondor•apana.org.au>,
Paul Mackerras <paulus@samba•org>,
Christoph Lameter <clameter@sgi•com>,
Chris Snook <csnook@redhat•com>,
Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
linux-arch@vger•kernel.org,
Linus Torvalds <torvalds@linux-foundation•org>,
netdev@vger•kernel.org, Andrew Morton <akpm@linux-foundation•org>,
ak@suse•de, heiko.carstens@de•ibm.com, davem@davemloft•net,
schwidefsky@de•ibm.com, wensong@linux-vs•org, horms@verge•net.au,
wjiang@resilience•com, cfriesen@nortel•com, zlynx@acm•org,
rpjday@mindspring•com, jesper.juhl@gmail•com,
segher@kernel•crashing.org
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
Date: Fri, 17 Aug 2007 22:56:41 +1000 [thread overview]
Message-ID: <46C59B09.8040004@cyberone.com.au> (raw)
In-Reply-To: <alpine.LFD.0.999.0708171737060.3666@enigma.security.iitk.ac.in>
Satyam Sharma wrote:
>
>On Fri, 17 Aug 2007, Nick Piggin wrote:
>
>
>>Satyam Sharma wrote:
>>
>>>On Fri, 17 Aug 2007, Nick Piggin wrote:
>>>
>>>>Satyam Sharma wrote:
>>>>
>>>>It is very obvious. msleep calls schedule() (ie. sleeps), which is
>>>>always a barrier.
>>>>
>>>Probably you didn't mean that, but no, schedule() is not barrier because
>>>it sleeps. It's a barrier because it's invisible.
>>>
>>Where did I say it is a barrier because it sleeps?
>>
>
>Just below. What you wrote:
>
>
>>It is always a barrier because, at the lowest level, schedule() (and thus
>>anything that sleeps) is defined to always be a barrier.
>>
>
>"It is always a barrier because, at the lowest level, anything that sleeps
>is defined to always be a barrier".
>
... because it must call schedule and schedule is a barrier.
>>Regardless of
>>whatever obscure means the compiler might need to infer the barrier.
>>
>>In other words, you can ignore those obscure details because schedule() is
>>always going to have an explicit barrier in it.
>>
>
>I didn't quite understand what you said here, so I'll tell what I think:
>
>* foo() is a compiler barrier if the definition of foo() is invisible to
> the compiler at a callsite.
>
>* foo() is also a compiler barrier if the definition of foo() includes
> a barrier, and it is inlined at the callsite.
>
>If the above is wrong, or if there's something else at play as well,
>do let me know.
>
Right.
>>>>The "unobvious" thing is that you wanted to know how the compiler knows
>>>>a function is a barrier -- answer is that if it does not *know* it is not
>>>>a barrier, it must assume it is a barrier.
>>>>
>>>True, that's clearly what happens here. But are you're definitely joking
>>>that this is "obvious" in terms of code-clarity, right?
>>>
>>No. If you accept that barrier() is implemented correctly, and you know
>>that sleeping is defined to be a barrier,
>>
>
>Curiously, that's the second time you've said "sleeping is defined to
>be a (compiler) barrier".
>
_In Linux,_ sleeping is defined to be a compiler barrier.
>How does the compiler even know if foo() is
>a function that "sleeps"? Do compilers have some notion of "sleeping"
>to ensure they automatically assume a compiler barrier whenever such
>a function is called? Or are you saying that the compiler can see the
>barrier() inside said function ... nopes, you're saying quite the
>opposite below.
>
You're getting too worried about the compiler implementation. Start
by assuming that it does work ;)
>>then its perfectly clear. You
>>don't have to know how the compiler "knows" that some function contains
>>a barrier.
>>
>
>I think I do, why not? Would appreciate if you could elaborate on this.
>
If a function is not completely visible to the compiler (so it can't
determine whether a barrier could be in it or not), then it must always
assume it will contain a barrier so it always does the right thing.
next prev parent reply other threads:[~2007-08-17 12:56 UTC|newest]
Thread overview: 308+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-09 13:14 [PATCH 0/24] make atomic_read() behave consistently across all architectures Chris Snook
2007-08-09 12:41 ` Arnd Bergmann
2007-08-09 14:29 ` Chris Snook
2007-08-09 15:30 ` Arnd Bergmann
2007-08-14 22:31 ` Christoph Lameter
2007-08-14 22:45 ` Chris Snook
2007-08-14 22:51 ` Christoph Lameter
2007-08-14 23:08 ` Satyam Sharma
2007-08-14 23:04 ` Chris Snook
2007-08-14 23:14 ` Christoph Lameter
2007-08-15 6:49 ` Herbert Xu
2007-08-15 8:18 ` Heiko Carstens
2007-08-15 13:53 ` Stefan Richter
2007-08-15 14:35 ` Satyam Sharma
2007-08-15 14:52 ` Herbert Xu
2007-08-15 16:09 ` Stefan Richter
2007-08-15 16:27 ` Paul E. McKenney
2007-08-15 17:13 ` Satyam Sharma
2007-08-15 18:31 ` Segher Boessenkool
2007-08-15 18:57 ` Paul E. McKenney
2007-08-15 19:54 ` Satyam Sharma
2007-08-15 20:17 ` Paul E. McKenney
2007-08-15 20:52 ` Segher Boessenkool
2007-08-15 22:42 ` Paul E. McKenney
2007-08-15 20:47 ` Segher Boessenkool
2007-08-16 0:36 ` (unknown) Satyam Sharma
2007-08-16 0:32 ` your mail Herbert Xu
2007-08-16 0:58 ` [PATCH 0/24] make atomic_read() behave consistently across all architectures Satyam Sharma
2007-08-16 0:51 ` Herbert Xu
2007-08-16 1:18 ` Satyam Sharma
2007-08-16 1:38 ` Segher Boessenkool
2007-08-15 21:05 ` [PATCH 0/24] make atomic_read() behave consistently across all architectures Segher Boessenkool
2007-08-15 22:44 ` Paul E. McKenney
2007-08-16 1:23 ` Segher Boessenkool
2007-08-16 2:22 ` Paul E. McKenney
2007-08-16 0:39 ` [PATCH] i386: Fix a couple busy loops in mach_wakecpu.h:wait_for_init_deassert() Satyam Sharma
2007-08-24 11:59 ` Denys Vlasenko
2007-08-24 12:07 ` Andi Kleen
2007-08-24 12:12 ` Kenn Humborg
2007-08-24 14:25 ` Denys Vlasenko
2007-08-24 17:34 ` Linus Torvalds
2007-08-24 13:30 ` Satyam Sharma
2007-08-24 17:06 ` Christoph Lameter
2007-08-24 20:26 ` Denys Vlasenko
2007-08-24 20:34 ` Chris Snook
2007-08-24 16:19 ` Luck, Tony
2007-08-15 16:13 ` [PATCH 0/24] make atomic_read() behave consistently across all architectures Chris Snook
2007-08-15 23:40 ` Herbert Xu
2007-08-15 23:51 ` Paul E. McKenney
2007-08-16 1:30 ` Segher Boessenkool
2007-08-16 2:30 ` Paul E. McKenney
2007-08-16 19:33 ` Segher Boessenkool
2007-08-16 1:26 ` Segher Boessenkool
2007-08-16 2:23 ` Nick Piggin
2007-08-16 19:32 ` Segher Boessenkool
2007-08-17 2:19 ` Nick Piggin
2007-08-17 3:16 ` Paul Mackerras
2007-08-17 3:32 ` Nick Piggin
2007-08-17 3:50 ` Linus Torvalds
2007-08-17 23:59 ` Paul E. McKenney
2007-08-18 0:09 ` Herbert Xu
2007-08-18 1:08 ` Paul E. McKenney
2007-08-18 1:24 ` Christoph Lameter
2007-08-18 1:41 ` Satyam Sharma
2007-08-18 4:13 ` Linus Torvalds
2007-08-18 13:36 ` Satyam Sharma
2007-08-18 21:54 ` Paul E. McKenney
2007-08-18 22:41 ` Linus Torvalds
2007-08-18 23:19 ` Paul E. McKenney
2007-08-24 12:19 ` Denys Vlasenko
2007-08-24 17:19 ` Linus Torvalds
2007-08-18 21:56 ` Paul E. McKenney
2007-08-20 13:31 ` Chris Snook
2007-08-20 22:04 ` Segher Boessenkool
2007-08-20 22:48 ` Russell King
2007-08-20 23:02 ` Segher Boessenkool
2007-08-21 0:05 ` Paul E. McKenney
2007-08-21 7:08 ` Russell King
2007-08-21 7:05 ` Russell King
2007-08-21 9:33 ` Paul Mackerras
2007-08-21 11:37 ` Andi Kleen
2007-08-21 14:48 ` Segher Boessenkool
2007-08-21 16:16 ` Paul E. McKenney
2007-08-21 22:51 ` Valdis.Kletnieks
2007-08-22 0:50 ` Paul E. McKenney
2007-08-22 21:38 ` Adrian Bunk
2007-08-21 14:39 ` Segher Boessenkool
2007-08-17 3:42 ` Linus Torvalds
2007-08-17 5:18 ` Paul E. McKenney
2007-08-17 5:56 ` Satyam Sharma
2007-08-17 7:26 ` Nick Piggin
2007-08-17 8:47 ` Satyam Sharma
2007-08-17 9:15 ` Nick Piggin
2007-08-17 10:12 ` Satyam Sharma
2007-08-17 12:14 ` Nick Piggin
2007-08-17 13:05 ` Satyam Sharma
2007-08-17 9:48 ` Paul Mackerras
2007-08-17 10:23 ` Satyam Sharma
2007-08-17 22:49 ` Segher Boessenkool
2007-08-17 23:51 ` Satyam Sharma
2007-08-17 23:55 ` Segher Boessenkool
2007-08-17 6:42 ` Geert Uytterhoeven
2007-08-17 8:52 ` Andi Kleen
2007-08-17 10:08 ` Satyam Sharma
2007-08-17 22:29 ` Segher Boessenkool
2007-08-17 17:37 ` Segher Boessenkool
2007-08-14 23:26 ` Paul E. McKenney
2007-08-15 10:35 ` Stefan Richter
2007-08-15 12:04 ` Herbert Xu
2007-08-15 12:31 ` Satyam Sharma
2007-08-15 13:08 ` Stefan Richter
2007-08-15 13:11 ` Stefan Richter
2007-08-15 13:47 ` Satyam Sharma
2007-08-15 14:25 ` Paul E. McKenney
2007-08-15 15:33 ` Herbert Xu
2007-08-15 16:08 ` Paul E. McKenney
2007-08-15 17:18 ` Satyam Sharma
2007-08-15 17:33 ` Paul E. McKenney
2007-08-15 18:05 ` Satyam Sharma
2007-08-15 18:19 ` David Howells
2007-08-15 18:45 ` Paul E. McKenney
2007-08-15 23:41 ` Herbert Xu
2007-08-15 23:53 ` Paul E. McKenney
2007-08-16 0:12 ` Herbert Xu
2007-08-16 0:23 ` Paul E. McKenney
2007-08-16 0:30 ` Herbert Xu
2007-08-16 0:49 ` Paul E. McKenney
2007-08-16 0:53 ` Herbert Xu
2007-08-16 1:14 ` Paul E. McKenney
2007-08-15 17:55 ` Satyam Sharma
2007-08-15 19:07 ` Paul E. McKenney
2007-08-15 21:07 ` Segher Boessenkool
2007-08-15 20:58 ` Segher Boessenkool
2007-08-15 18:31 ` Segher Boessenkool
2007-08-15 19:40 ` Satyam Sharma
2007-08-15 20:42 ` Segher Boessenkool
2007-08-16 1:23 ` Satyam Sharma
2007-08-15 23:22 ` Paul Mackerras
2007-08-16 0:26 ` Christoph Lameter
2007-08-16 0:34 ` Paul Mackerras
2007-08-16 0:40 ` Christoph Lameter
2007-08-16 0:39 ` Paul E. McKenney
2007-08-16 0:42 ` Christoph Lameter
2007-08-16 0:53 ` Paul E. McKenney
2007-08-16 0:59 ` Christoph Lameter
2007-08-16 1:14 ` Paul E. McKenney
2007-08-16 1:41 ` Christoph Lameter
2007-08-16 2:15 ` Satyam Sharma
2007-08-16 2:08 ` Herbert Xu
2007-08-16 2:18 ` Christoph Lameter
2007-08-16 3:23 ` Paul Mackerras
2007-08-16 3:33 ` Herbert Xu
2007-08-16 3:48 ` Paul Mackerras
2007-08-16 4:03 ` Herbert Xu
2007-08-16 4:34 ` Paul Mackerras
2007-08-16 5:37 ` Herbert Xu
2007-08-16 6:00 ` Paul Mackerras
2007-08-16 18:50 ` Christoph Lameter
2007-08-16 18:48 ` Christoph Lameter
2007-08-16 19:44 ` Segher Boessenkool
2007-08-16 2:18 ` Chris Friesen
2007-08-16 2:32 ` Paul E. McKenney
2007-08-16 1:51 ` Paul Mackerras
2007-08-16 2:00 ` Herbert Xu
2007-08-16 2:05 ` Paul Mackerras
2007-08-16 2:11 ` Herbert Xu
2007-08-16 2:35 ` Paul E. McKenney
2007-08-16 3:15 ` Paul Mackerras
2007-08-16 3:43 ` Herbert Xu
2007-08-16 2:15 ` Christoph Lameter
2007-08-16 2:17 ` Christoph Lameter
2007-08-16 2:33 ` Satyam Sharma
2007-08-16 3:01 ` Satyam Sharma
2007-08-16 4:11 ` Paul Mackerras
2007-08-16 5:39 ` Herbert Xu
2007-08-16 6:56 ` Paul Mackerras
2007-08-16 7:09 ` Herbert Xu
2007-08-16 8:06 ` Stefan Richter
2007-08-16 8:10 ` Herbert Xu
2007-08-16 9:54 ` Stefan Richter
2007-08-16 10:31 ` Stefan Richter
2007-08-16 10:42 ` Herbert Xu
2007-08-16 16:34 ` Paul E. McKenney
2007-08-16 23:59 ` Herbert Xu
2007-08-17 1:01 ` Paul E. McKenney
2007-08-17 7:39 ` Satyam Sharma
2007-08-17 14:31 ` Paul E. McKenney
2007-08-17 18:31 ` Satyam Sharma
2007-08-17 18:56 ` Paul E. McKenney
2007-08-17 3:15 ` Nick Piggin
2007-08-17 4:02 ` Paul Mackerras
2007-08-17 4:39 ` Nick Piggin
2007-08-17 7:25 ` Stefan Richter
2007-08-17 8:06 ` Nick Piggin
2007-08-17 8:58 ` Satyam Sharma
2007-08-17 9:15 ` Nick Piggin
2007-08-17 10:03 ` Satyam Sharma
2007-08-17 11:50 ` Nick Piggin
2007-08-17 12:50 ` Satyam Sharma
2007-08-17 12:56 ` Nick Piggin [this message]
2007-08-18 2:15 ` Satyam Sharma
2007-08-17 10:48 ` Stefan Richter
2007-08-17 10:58 ` Stefan Richter
2007-08-18 14:35 ` LDD3 pitfalls (was Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures) Stefan Richter
2007-08-20 13:28 ` Chris Snook
2007-08-17 22:14 ` [PATCH 0/24] make atomic_read() behave consistently across all architectures Segher Boessenkool
2007-08-17 5:04 ` Paul Mackerras
2007-08-16 10:35 ` Herbert Xu
2007-08-16 19:48 ` Chris Snook
2007-08-17 0:02 ` Herbert Xu
2007-08-17 2:04 ` Chris Snook
2007-08-17 2:13 ` Herbert Xu
2007-08-17 2:31 ` Nick Piggin
2007-08-17 5:09 ` Paul Mackerras
2007-08-17 5:32 ` Herbert Xu
2007-08-17 5:41 ` Paul Mackerras
2007-08-17 8:28 ` Satyam Sharma
2007-08-16 14:48 ` Ilpo Järvinen
2007-08-16 16:19 ` Stefan Richter
2007-08-16 19:55 ` Chris Snook
2007-08-16 20:20 ` Christoph Lameter
2007-08-17 1:02 ` Paul E. McKenney
2007-08-17 1:28 ` Herbert Xu
2007-08-17 5:07 ` Paul E. McKenney
2007-08-17 2:16 ` Paul Mackerras
2007-08-17 3:03 ` Linus Torvalds
2007-08-17 3:43 ` Paul Mackerras
2007-08-17 3:53 ` Herbert Xu
2007-08-17 6:26 ` Satyam Sharma
2007-08-17 8:38 ` Nick Piggin
2007-08-17 9:14 ` Satyam Sharma
2007-08-17 9:31 ` Nick Piggin
2007-08-17 10:55 ` Satyam Sharma
2007-08-17 12:39 ` Nick Piggin
2007-08-17 13:36 ` Satyam Sharma
2007-08-17 16:48 ` Linus Torvalds
2007-08-17 18:50 ` Chris Friesen
2007-08-17 18:54 ` Arjan van de Ven
2007-08-17 19:49 ` Paul E. McKenney
2007-08-17 19:49 ` Arjan van de Ven
2007-08-17 20:12 ` Paul E. McKenney
2007-08-17 19:08 ` Linus Torvalds
2007-08-20 13:15 ` Chris Snook
2007-08-20 13:32 ` Herbert Xu
2007-08-20 13:38 ` Chris Snook
2007-08-20 22:07 ` Segher Boessenkool
2007-08-21 5:46 ` Linus Torvalds
2007-08-21 7:04 ` David Miller
2007-08-21 13:50 ` Chris Snook
2007-08-21 14:59 ` Segher Boessenkool
2007-08-21 16:31 ` Satyam Sharma
2007-08-21 16:43 ` Linus Torvalds
2007-09-09 18:02 ` Denys Vlasenko
2007-09-09 18:18 ` Arjan van de Ven
2007-09-10 10:56 ` Denys Vlasenko
2007-09-10 11:15 ` Herbert Xu
2007-09-10 12:22 ` Kyle Moffett
2007-09-10 13:38 ` Denys Vlasenko
2007-09-10 14:16 ` Denys Vlasenko
2007-09-10 15:09 ` Linus Torvalds
2007-09-10 16:46 ` Denys Vlasenko
2007-09-10 19:59 ` Kyle Moffett
2007-09-10 18:59 ` Christoph Lameter
2007-09-10 23:19 ` [PATCH] Document non-semantics of atomic_read() and atomic_set() Chris Snook
2007-09-10 23:44 ` Paul E. McKenney
2007-09-11 19:35 ` Christoph Lameter
2007-09-10 14:51 ` [PATCH 0/24] make atomic_read() behave consistently across all architectures Arjan van de Ven
2007-09-10 14:38 ` Denys Vlasenko
2007-09-10 17:02 ` Arjan van de Ven
2007-08-17 11:08 ` Stefan Richter
2007-08-17 22:09 ` Segher Boessenkool
2007-08-17 17:41 ` Segher Boessenkool
2007-08-17 18:38 ` Satyam Sharma
2007-08-17 23:17 ` Segher Boessenkool
2007-08-17 23:55 ` Satyam Sharma
2007-08-18 0:04 ` Segher Boessenkool
2007-08-18 1:56 ` Satyam Sharma
2007-08-18 2:15 ` Segher Boessenkool
2007-08-18 3:33 ` Satyam Sharma
2007-08-18 5:18 ` Segher Boessenkool
2007-08-18 13:20 ` Satyam Sharma
2007-09-10 18:59 ` Christoph Lameter
2007-09-10 20:54 ` Paul E. McKenney
2007-09-10 21:36 ` Christoph Lameter
2007-09-10 21:50 ` Paul E. McKenney
2007-09-11 2:27 ` Segher Boessenkool
2007-08-16 21:08 ` Luck, Tony
2007-08-16 19:55 ` Chris Snook
2007-08-16 18:54 ` Christoph Lameter
2007-08-16 20:07 ` Paul E. McKenney
2007-08-16 3:05 ` Paul Mackerras
2007-08-16 19:39 ` Segher Boessenkool
2007-08-16 2:07 ` Segher Boessenkool
2007-08-24 12:50 ` Denys Vlasenko
2007-08-24 17:15 ` Christoph Lameter
2007-08-24 20:21 ` Denys Vlasenko
2007-08-16 3:37 ` Bill Fink
2007-08-16 5:20 ` Satyam Sharma
2007-08-16 5:57 ` Satyam Sharma
2007-08-16 9:25 ` Satyam Sharma
2007-08-16 21:00 ` Segher Boessenkool
2007-08-17 4:32 ` Satyam Sharma
2007-08-17 22:38 ` Segher Boessenkool
2007-08-18 14:42 ` Satyam Sharma
2007-08-16 20:50 ` Segher Boessenkool
2007-08-17 4:24 ` Satyam Sharma
2007-08-17 22:34 ` Segher Boessenkool
2007-08-15 19:59 ` Christoph Lameter
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