On Sat, Feb 15, 2014 at 9:30 AM, Torvald Riegel wrote:
>
> I think the example is easy to misunderstand, because the context isn't
> clear. Therefore, let me first try to clarify the background.
>
> (1) The abstract machine does not write speculatively.
> (2) Emitting a branch instruction and
On Sat, Feb 15, 2014 at 9:45 AM, Torvald Riegel wrote:
>
> I think a major benefit of C11's memory model is that it gives a
> *precise* specification for how a compiler is allowed to optimize.
Clearly it does *not*. This whole discussion is proof of that. It's
not at all clear, and the standard
On Fri, 2014-02-14 at 18:44 -0800, Linus Torvalds wrote:
> On Fri, Feb 14, 2014 at 6:08 PM, Paul E. McKenney
> wrote:
> >
> > One way of looking at the discussion between Torvald and myself would be
> > as a seller (Torvald) and a buyer (me) haggling over the fine print in
> > a proposed contract
On Fri, 2014-02-14 at 12:02 -0800, Linus Torvalds wrote:
> On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
> wrote:
> >
> > Why are we still discussing this idiocy? It's irrelevant. If the
> > standard really allows random store speculation, the standard doesn't
> > matter, and sane people
On Fri, 2014-02-14 at 11:50 -0800, Linus Torvalds wrote:
> On Fri, Feb 14, 2014 at 9:29 AM, Paul E. McKenney
> wrote:
> >
> > Linus, Peter, any objections to marking places where we are relying on
> > ordering from control dependencies against later stores? This approach
> > seems to me to have
On Fri, 2014-02-14 at 11:50 -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 9:29 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Linus, Peter, any objections to marking places where we are relying on
ordering from control dependencies against later stores? This approach
On Fri, 2014-02-14 at 12:02 -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
torva...@linux-foundation.org wrote:
Why are we still discussing this idiocy? It's irrelevant. If the
standard really allows random store speculation, the standard doesn't
matter,
On Fri, 2014-02-14 at 18:44 -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 6:08 PM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
One way of looking at the discussion between Torvald and myself would be
as a seller (Torvald) and a buyer (me) haggling over the fine print in
a
On Sat, Feb 15, 2014 at 9:45 AM, Torvald Riegel trie...@redhat.com wrote:
I think a major benefit of C11's memory model is that it gives a
*precise* specification for how a compiler is allowed to optimize.
Clearly it does *not*. This whole discussion is proof of that. It's
not at all clear,
On Sat, Feb 15, 2014 at 9:30 AM, Torvald Riegel trie...@redhat.com wrote:
I think the example is easy to misunderstand, because the context isn't
clear. Therefore, let me first try to clarify the background.
(1) The abstract machine does not write speculatively.
(2) Emitting a branch
On Fri, Feb 14, 2014 at 10:35:44PM -0800, Paul E. McKenney wrote:
> On Fri, Feb 14, 2014 at 06:48:02PM -0800, Linus Torvalds wrote:
> > On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
> > wrote:
> > >
> > > And conversely, the C11 people can walk away from us too. But if they
> > > can't make us
On Fri, Feb 14, 2014 at 06:48:02PM -0800, Linus Torvalds wrote:
> On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
> wrote:
> >
> > And conversely, the C11 people can walk away from us too. But if they
> > can't make us happy (and by "make us happy", I really mean no stupid
> > games on our part)
On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
wrote:
>
> And conversely, the C11 people can walk away from us too. But if they
> can't make us happy (and by "make us happy", I really mean no stupid
> games on our part) I personally think they'll have a stronger
> standard, and a real use case,
On Fri, Feb 14, 2014 at 6:08 PM, Paul E. McKenney
wrote:
>
> One way of looking at the discussion between Torvald and myself would be
> as a seller (Torvald) and a buyer (me) haggling over the fine print in
> a proposed contract (the standard). Whether that makes you feel better
> or worse about
On Fri, Feb 14, 2014 at 12:02:23PM -0800, Linus Torvalds wrote:
> On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
> wrote:
> >
> > Why are we still discussing this idiocy? It's irrelevant. If the
> > standard really allows random store speculation, the standard doesn't
> > matter, and sane
On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
wrote:
>
> Why are we still discussing this idiocy? It's irrelevant. If the
> standard really allows random store speculation, the standard doesn't
> matter, and sane people shouldn't waste their time arguing about it.
Btw, the other part of this
On Fri, Feb 14, 2014 at 9:29 AM, Paul E. McKenney
wrote:
>
> Linus, Peter, any objections to marking places where we are relying on
> ordering from control dependencies against later stores? This approach
> seems to me to have significant documentation benefits.
Quite frankly, I think it's
On Fri, 2014-02-14 at 09:29 -0800, Paul E. McKenney wrote:
> On Thu, Feb 13, 2014 at 08:43:01PM -0800, Torvald Riegel wrote:
> > On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
>
> [ . . . ]
>
> > > Another option would be to flag the conditional expression, prohibiting
> > > the
On Fri, 2014-02-14 at 10:50 +0100, Peter Zijlstra wrote:
> On Thu, Feb 13, 2014 at 09:07:55PM -0800, Torvald Riegel wrote:
> > That depends on what your goal is.
First, I don't know why you quoted that, but without the context,
quoting it doesn't make sense. Let me repeat the point. The
On Thu, Feb 13, 2014 at 08:43:01PM -0800, Torvald Riegel wrote:
> On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
[ . . . ]
> > Another option would be to flag the conditional expression, prohibiting
> > the compiler from optimizing out any conditional branches. Perhaps
> > something
On Thu, Feb 13, 2014 at 09:07:55PM -0800, Torvald Riegel wrote:
> That depends on what your goal is.
A compiler that we don't need to fight in order to generate sane code
would be nice. But as Linus said; we can continue to ignore you lot and
go on as we've done.
--
To unsubscribe from this list:
On Thu, Feb 13, 2014 at 09:07:55PM -0800, Torvald Riegel wrote:
That depends on what your goal is.
A compiler that we don't need to fight in order to generate sane code
would be nice. But as Linus said; we can continue to ignore you lot and
go on as we've done.
--
To unsubscribe from this list:
On Thu, Feb 13, 2014 at 08:43:01PM -0800, Torvald Riegel wrote:
On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
[ . . . ]
Another option would be to flag the conditional expression, prohibiting
the compiler from optimizing out any conditional branches. Perhaps
something like
On Fri, 2014-02-14 at 10:50 +0100, Peter Zijlstra wrote:
On Thu, Feb 13, 2014 at 09:07:55PM -0800, Torvald Riegel wrote:
That depends on what your goal is.
First, I don't know why you quoted that, but without the context,
quoting it doesn't make sense. Let me repeat the point. The standard
On Fri, 2014-02-14 at 09:29 -0800, Paul E. McKenney wrote:
On Thu, Feb 13, 2014 at 08:43:01PM -0800, Torvald Riegel wrote:
On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
[ . . . ]
Another option would be to flag the conditional expression, prohibiting
the compiler from
On Fri, Feb 14, 2014 at 9:29 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Linus, Peter, any objections to marking places where we are relying on
ordering from control dependencies against later stores? This approach
seems to me to have significant documentation benefits.
Quite
On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
torva...@linux-foundation.org wrote:
Why are we still discussing this idiocy? It's irrelevant. If the
standard really allows random store speculation, the standard doesn't
matter, and sane people shouldn't waste their time arguing about it.
On Fri, Feb 14, 2014 at 12:02:23PM -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 11:50 AM, Linus Torvalds
torva...@linux-foundation.org wrote:
Why are we still discussing this idiocy? It's irrelevant. If the
standard really allows random store speculation, the standard doesn't
On Fri, Feb 14, 2014 at 6:08 PM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
One way of looking at the discussion between Torvald and myself would be
as a seller (Torvald) and a buyer (me) haggling over the fine print in
a proposed contract (the standard). Whether that makes you feel
On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
torva...@linux-foundation.org wrote:
And conversely, the C11 people can walk away from us too. But if they
can't make us happy (and by make us happy, I really mean no stupid
games on our part) I personally think they'll have a stronger
standard,
On Fri, Feb 14, 2014 at 06:48:02PM -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
torva...@linux-foundation.org wrote:
And conversely, the C11 people can walk away from us too. But if they
can't make us happy (and by make us happy, I really mean no stupid
On Fri, Feb 14, 2014 at 10:35:44PM -0800, Paul E. McKenney wrote:
On Fri, Feb 14, 2014 at 06:48:02PM -0800, Linus Torvalds wrote:
On Fri, Feb 14, 2014 at 6:44 PM, Linus Torvalds
torva...@linux-foundation.org wrote:
And conversely, the C11 people can walk away from us too. But if they
On Wed, 2014-02-12 at 10:19 +0100, Peter Zijlstra wrote:
> > I don't know the specifics of your example, but from how I understand
> > it, I don't see a problem if the compiler can prove that the store will
> > always happen.
> >
> > To be more specific, if the compiler can prove that the store
On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
> On Thu, Feb 13, 2014 at 12:03:57PM -0800, Torvald Riegel wrote:
> > On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
> > > On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
> > > > On Wed, Feb 12, 2014 at 10:07
On Thu, Feb 13, 2014 at 12:03:57PM -0800, Torvald Riegel wrote:
> On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
> > On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
> > > On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
> > > wrote:
> > > >
> > > > Us Linux-kernel
On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
> On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
> > On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
> > wrote:
> > >
> > > Us Linux-kernel hackers will often need to use volatile semantics in
> > > combination with
On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Us Linux-kernel hackers will often need to use volatile semantics in
On Thu, Feb 13, 2014 at 12:03:57PM -0800, Torvald Riegel wrote:
On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Us
On Thu, 2014-02-13 at 18:01 -0800, Paul E. McKenney wrote:
On Thu, Feb 13, 2014 at 12:03:57PM -0800, Torvald Riegel wrote:
On Wed, 2014-02-12 at 16:23 -0800, Paul E. McKenney wrote:
On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
On Wed, Feb 12, 2014 at 10:07 AM, Paul E.
On Wed, 2014-02-12 at 10:19 +0100, Peter Zijlstra wrote:
I don't know the specifics of your example, but from how I understand
it, I don't see a problem if the compiler can prove that the store will
always happen.
To be more specific, if the compiler can prove that the store will
On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
> On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
> wrote:
> >
> > Us Linux-kernel hackers will often need to use volatile semantics in
> > combination with C11 atomics in most cases. The C11 atomics do cover
> > some of the
On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
wrote:
>
> Us Linux-kernel hackers will often need to use volatile semantics in
> combination with C11 atomics in most cases. The C11 atomics do cover
> some of the reasons we currently use ACCESS_ONCE(), but not all of them --
> in particular,
On Tue, Feb 11, 2014 at 09:13:34PM -0800, Torvald Riegel wrote:
> On Sun, 2014-02-09 at 19:51 -0800, Paul E. McKenney wrote:
> > On Mon, Feb 10, 2014 at 01:06:48AM +0100, Torvald Riegel wrote:
> > > On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
> > > > On Fri, Feb 07, 2014 at
On Tue, Feb 11, 2014 at 09:39:24PM -0800, Torvald Riegel wrote:
> On Mon, 2014-02-10 at 11:09 -0800, Linus Torvalds wrote:
> > On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> > >
> > > Intuitively, this is wrong because this let's the program take a step
> > > the abstract machine
On Wed, Feb 12, 2014 at 09:42:09AM -0800, Paul E. McKenney wrote:
> You need volatile semantics to force the compiler to ignore any proofs
> it might otherwise attempt to construct. Hence all the ACCESS_ONCE()
> calls in my email to Torvald. (Hopefully I translated your example
> reasonably.)
On Tue, Feb 11, 2014 at 10:06:34PM -0800, Torvald Riegel wrote:
> On Tue, 2014-02-11 at 07:59 -0800, Paul E. McKenney wrote:
> > On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
> > > On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> > > >
> > > > Intuitively, this is wrong
On Wed, Feb 12, 2014 at 10:19:07AM +0100, Peter Zijlstra wrote:
> > I don't know the specifics of your example, but from how I understand
> > it, I don't see a problem if the compiler can prove that the store will
> > always happen.
> >
> > To be more specific, if the compiler can prove that the
> I don't know the specifics of your example, but from how I understand
> it, I don't see a problem if the compiler can prove that the store will
> always happen.
>
> To be more specific, if the compiler can prove that the store will
> happen anyway, and the region of code can be assumed to
I don't know the specifics of your example, but from how I understand
it, I don't see a problem if the compiler can prove that the store will
always happen.
To be more specific, if the compiler can prove that the store will
happen anyway, and the region of code can be assumed to always run
On Wed, Feb 12, 2014 at 10:19:07AM +0100, Peter Zijlstra wrote:
I don't know the specifics of your example, but from how I understand
it, I don't see a problem if the compiler can prove that the store will
always happen.
To be more specific, if the compiler can prove that the store will
On Tue, Feb 11, 2014 at 10:06:34PM -0800, Torvald Riegel wrote:
On Tue, 2014-02-11 at 07:59 -0800, Paul E. McKenney wrote:
On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is
On Wed, Feb 12, 2014 at 09:42:09AM -0800, Paul E. McKenney wrote:
You need volatile semantics to force the compiler to ignore any proofs
it might otherwise attempt to construct. Hence all the ACCESS_ONCE()
calls in my email to Torvald. (Hopefully I translated your example
reasonably.)
My
On Tue, Feb 11, 2014 at 09:39:24PM -0800, Torvald Riegel wrote:
On Mon, 2014-02-10 at 11:09 -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is wrong because this let's the program take a step
the abstract machine
On Tue, Feb 11, 2014 at 09:13:34PM -0800, Torvald Riegel wrote:
On Sun, 2014-02-09 at 19:51 -0800, Paul E. McKenney wrote:
On Mon, Feb 10, 2014 at 01:06:48AM +0100, Torvald Riegel wrote:
On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 12:44:48AM +0100,
On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Us Linux-kernel hackers will often need to use volatile semantics in
combination with C11 atomics in most cases. The C11 atomics do cover
some of the reasons we currently use ACCESS_ONCE(), but not all of
On Wed, Feb 12, 2014 at 12:22:53PM -0800, Linus Torvalds wrote:
On Wed, Feb 12, 2014 at 10:07 AM, Paul E. McKenney
paul...@linux.vnet.ibm.com wrote:
Us Linux-kernel hackers will often need to use volatile semantics in
combination with C11 atomics in most cases. The C11 atomics do cover
On Tue, 2014-02-11 at 07:59 -0800, Paul E. McKenney wrote:
> On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
> > On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> > >
> > > Intuitively, this is wrong because this let's the program take a step
> > > the abstract machine
On Mon, 2014-02-10 at 11:09 -0800, Linus Torvalds wrote:
> On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> >
> > Intuitively, this is wrong because this let's the program take a step
> > the abstract machine wouldn't do. This is different to the sequential
> > code that Peter posted
On Sun, 2014-02-09 at 19:51 -0800, Paul E. McKenney wrote:
> On Mon, Feb 10, 2014 at 01:06:48AM +0100, Torvald Riegel wrote:
> > On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
> > > On Fri, Feb 07, 2014 at 12:44:48AM +0100, Torvald Riegel wrote:
> > > > On Thu, 2014-02-06 at 14:11
On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
> On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> >
> > Intuitively, this is wrong because this let's the program take a step
> > the abstract machine wouldn't do. This is different to the sequential
> > code that Peter
On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is wrong because this let's the program take a step
the abstract machine wouldn't do. This is different to the sequential
code that
On Sun, 2014-02-09 at 19:51 -0800, Paul E. McKenney wrote:
On Mon, Feb 10, 2014 at 01:06:48AM +0100, Torvald Riegel wrote:
On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 12:44:48AM +0100, Torvald Riegel wrote:
On Thu, 2014-02-06 at 14:11 -0800, Paul E.
On Mon, 2014-02-10 at 11:09 -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is wrong because this let's the program take a step
the abstract machine wouldn't do. This is different to the sequential
code that Peter
On Tue, 2014-02-11 at 07:59 -0800, Paul E. McKenney wrote:
On Mon, Feb 10, 2014 at 11:09:24AM -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is wrong because this let's the program take a step
the abstract machine
On Mon, Feb 10, 2014 at 04:08:11PM -0500, Chris Metcalf wrote:
> (+LKML again)
>
> On 2/10/2014 3:57 PM, Peter Zijlstra wrote:
> > On Mon, Feb 10, 2014 at 03:50:04PM -0500, Chris Metcalf wrote:
> >> On 2/6/2014 8:52 AM, Peter Zijlstra wrote:
> >>> Its been compiled on everything I have a compiler
(+LKML again)
On 2/10/2014 3:57 PM, Peter Zijlstra wrote:
> On Mon, Feb 10, 2014 at 03:50:04PM -0500, Chris Metcalf wrote:
>> On 2/6/2014 8:52 AM, Peter Zijlstra wrote:
>>> Its been compiled on everything I have a compiler for, however frv and
>>> tile are missing because they're special and I
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
>
> Intuitively, this is wrong because this let's the program take a step
> the abstract machine wouldn't do. This is different to the sequential
> code that Peter posted because it uses atomics, and thus one can't
> easily assume that the
On Mon, Feb 10, 2014 at 03:04:43PM +, Paul E. McKenney wrote:
> On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
> > On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
> > > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > > > As near as I can
On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
> > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > > As near as I can tell, compiler writers hate the idea of prohibiting
> > > speculative-store
On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
> > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > > As near as I can tell, compiler writers hate the idea of prohibiting
> > > speculative-store
On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
> On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > As near as I can tell, compiler writers hate the idea of prohibiting
> > speculative-store optimizations because it requires them to introduce
> > both control
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> As near as I can tell, compiler writers hate the idea of prohibiting
> speculative-store optimizations because it requires them to introduce
> both control and data dependency tracking into their compilers. Many of
> them seem to
On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
> > Initial state: x == y == 0
> >
> > T1: r1 = atomic_load_explicit(x, memory_order_relaxed);
> > atomic_store_explicit(42, y, memory_order_relaxed);
> > if (r1 != 42)
> > atomic_store_explicit(r1, y,
On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
Initial state: x == y == 0
T1: r1 = atomic_load_explicit(x, memory_order_relaxed);
atomic_store_explicit(42, y, memory_order_relaxed);
if (r1 != 42)
atomic_store_explicit(r1, y, memory_order_relaxed);
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
As near as I can tell, compiler writers hate the idea of prohibiting
speculative-store optimizations because it requires them to introduce
both control and data dependency tracking into their compilers. Many of
them seem to
On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
As near as I can tell, compiler writers hate the idea of prohibiting
speculative-store optimizations because it requires them to introduce
both control and data
On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
As near as I can tell, compiler writers hate the idea of prohibiting
speculative-store
On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
As near as I can tell, compiler writers hate the idea of prohibiting
speculative-store
On Mon, Feb 10, 2014 at 03:04:43PM +, Paul E. McKenney wrote:
On Mon, Feb 10, 2014 at 11:49:29AM +, Will Deacon wrote:
On Mon, Feb 10, 2014 at 11:48:13AM +, Peter Zijlstra wrote:
On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
As near as I can tell, compiler
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
Intuitively, this is wrong because this let's the program take a step
the abstract machine wouldn't do. This is different to the sequential
code that Peter posted because it uses atomics, and thus one can't
easily
(+LKML again)
On 2/10/2014 3:57 PM, Peter Zijlstra wrote:
On Mon, Feb 10, 2014 at 03:50:04PM -0500, Chris Metcalf wrote:
On 2/6/2014 8:52 AM, Peter Zijlstra wrote:
Its been compiled on everything I have a compiler for, however frv and
tile are missing because they're special and I was tired.
On Mon, Feb 10, 2014 at 04:08:11PM -0500, Chris Metcalf wrote:
(+LKML again)
On 2/10/2014 3:57 PM, Peter Zijlstra wrote:
On Mon, Feb 10, 2014 at 03:50:04PM -0500, Chris Metcalf wrote:
On 2/6/2014 8:52 AM, Peter Zijlstra wrote:
Its been compiled on everything I have a compiler for,
On Mon, Feb 10, 2014 at 01:06:48AM +0100, Torvald Riegel wrote:
> On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
> > On Fri, Feb 07, 2014 at 12:44:48AM +0100, Torvald Riegel wrote:
> > > On Thu, 2014-02-06 at 14:11 -0800, Paul E. McKenney wrote:
> > > > On Thu, Feb 06, 2014 at
On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
> On Fri, 2014-02-07 at 10:02 -0800, Paul E. McKenney wrote:
> > On Fri, Feb 07, 2014 at 04:55:48PM +, Will Deacon wrote:
[ . . . ]
> > And then it is a short and uncontroversial step to the following:
> >
> > Initial state: x
On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
> On Fri, 2014-02-07 at 10:02 -0800, Paul E. McKenney wrote:
> > On Fri, Feb 07, 2014 at 04:55:48PM +, Will Deacon wrote:
> > > Hi Paul,
> > >
> > > On Fri, Feb 07, 2014 at 04:50:28PM +, Paul E. McKenney wrote:
> > > > On
On Sun, Feb 9, 2014 at 5:46 PM, Torvald Riegel wrote:
>
> IOW, I wrote that such a compiler transformation would be wrong in my
> opinion. Thus, it should *not* return 42.
Ahh, I am happy to have misunderstood. The "intuitively" threw me,
because I thought that was building up to a "but", and
On Sun, 2014-02-09 at 17:24 -0800, Linus Torvalds wrote:
> On Sun, Feb 9, 2014 at 5:16 PM, Torvald Riegel wrote:
> >
> > (a) seems to say that you don't like requiring programmers to mark
> > atomic accesses specially. Is that the case?
>
> In Paul's example, they were marked specially.
>
>
On Sun, Feb 9, 2014 at 5:16 PM, Torvald Riegel wrote:
>
> (a) seems to say that you don't like requiring programmers to mark
> atomic accesses specially. Is that the case?
In Paul's example, they were marked specially.
And you seemed to argue that Paul's example could possibly return
anything
On Sun, 2014-02-09 at 16:56 -0800, Linus Torvalds wrote:
> On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
> >
> > I wouldn't characterize the situation like this (although I can't speak
> > for others, obviously). IMHO, it's perfectly fine on sequential /
> > non-synchronizing code,
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel wrote:
>
> I wouldn't characterize the situation like this (although I can't speak
> for others, obviously). IMHO, it's perfectly fine on sequential /
> non-synchronizing code, because we know the difference isn't observable
> by a correct program.
On Fri, 2014-02-07 at 10:02 -0800, Paul E. McKenney wrote:
> On Fri, Feb 07, 2014 at 04:55:48PM +, Will Deacon wrote:
> > Hi Paul,
> >
> > On Fri, Feb 07, 2014 at 04:50:28PM +, Paul E. McKenney wrote:
> > > On Fri, Feb 07, 2014 at 08:44:05AM +0100, Peter Zijlstra wrote:
> > > > On Thu,
On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
> On Fri, Feb 07, 2014 at 12:44:48AM +0100, Torvald Riegel wrote:
> > On Thu, 2014-02-06 at 14:11 -0800, Paul E. McKenney wrote:
> > > On Thu, Feb 06, 2014 at 10:17:03PM +0100, Torvald Riegel wrote:
> > > > On Thu, 2014-02-06 at 11:27
On Thu, 2014-02-06 at 20:20 -0800, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 12:44:48AM +0100, Torvald Riegel wrote:
On Thu, 2014-02-06 at 14:11 -0800, Paul E. McKenney wrote:
On Thu, Feb 06, 2014 at 10:17:03PM +0100, Torvald Riegel wrote:
On Thu, 2014-02-06 at 11:27 -0800, Paul E.
On Fri, 2014-02-07 at 10:02 -0800, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 04:55:48PM +, Will Deacon wrote:
Hi Paul,
On Fri, Feb 07, 2014 at 04:50:28PM +, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 08:44:05AM +0100, Peter Zijlstra wrote:
On Thu, Feb 06, 2014 at
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
I wouldn't characterize the situation like this (although I can't speak
for others, obviously). IMHO, it's perfectly fine on sequential /
non-synchronizing code, because we know the difference isn't observable
by a
On Sun, 2014-02-09 at 16:56 -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 4:27 PM, Torvald Riegel trie...@redhat.com wrote:
I wouldn't characterize the situation like this (although I can't speak
for others, obviously). IMHO, it's perfectly fine on sequential /
non-synchronizing
On Sun, Feb 9, 2014 at 5:16 PM, Torvald Riegel trie...@redhat.com wrote:
(a) seems to say that you don't like requiring programmers to mark
atomic accesses specially. Is that the case?
In Paul's example, they were marked specially.
And you seemed to argue that Paul's example could possibly
On Sun, 2014-02-09 at 17:24 -0800, Linus Torvalds wrote:
On Sun, Feb 9, 2014 at 5:16 PM, Torvald Riegel trie...@redhat.com wrote:
(a) seems to say that you don't like requiring programmers to mark
atomic accesses specially. Is that the case?
In Paul's example, they were marked
On Sun, Feb 9, 2014 at 5:46 PM, Torvald Riegel trie...@redhat.com wrote:
IOW, I wrote that such a compiler transformation would be wrong in my
opinion. Thus, it should *not* return 42.
Ahh, I am happy to have misunderstood. The intuitively threw me,
because I thought that was building up to a
On Mon, Feb 10, 2014 at 01:27:51AM +0100, Torvald Riegel wrote:
On Fri, 2014-02-07 at 10:02 -0800, Paul E. McKenney wrote:
On Fri, Feb 07, 2014 at 04:55:48PM +, Will Deacon wrote:
Hi Paul,
On Fri, Feb 07, 2014 at 04:50:28PM +, Paul E. McKenney wrote:
On Fri, Feb 07, 2014
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