On Tue, Jul 04, 2023 at 04:25:45PM -0400, Alan Stern wrote:
> On Tue, Jul 04, 2023 at 01:19:23PM -0400, Olivier Dion wrote:
[ . . . ]
> > I am puzzled by this. Initialization of a shared variable does not need
> > to be atomic until its publication. Could you expand on this?
>
> In the kernel,
On Thu, Jul 04, 2019 at 01:00:18PM +0200, Richard Biener wrote:
> On Wed, Jul 3, 2019 at 6:33 PM Paul E. McKenney wrote:
> >
> > On Wed, Jul 03, 2019 at 05:47:56PM +0200, Richard Biener wrote:
> > > On July 3, 2019 5:14:58 PM GMT+02:00, "Paul E. McKenney"
&
On Wed, Jul 03, 2019 at 05:47:56PM +0200, Richard Biener wrote:
> On July 3, 2019 5:14:58 PM GMT+02:00, "Paul E. McKenney"
> wrote:
> >On Wed, Jul 03, 2019 at 12:39:41AM +0530, Akshat Garg wrote:
> >> On Tue, Jul 2, 2019 at 8:40 PM Paul E. McKenney
> >
&g
On Wed, Jul 03, 2019 at 12:39:41AM +0530, Akshat Garg wrote:
> On Tue, Jul 2, 2019 at 8:40 PM Paul E. McKenney
> wrote:
>
> > On Tue, Jul 02, 2019 at 02:15:55PM +0100, Ramana Radhakrishnan wrote:
> > > On Tue, Jul 2, 2019 at 1:38 PM Paul E. McKenney
> > wrote:
>
On Tue, Jul 02, 2019 at 07:53:20PM +0200, Richard Biener wrote:
> On July 2, 2019 5:36:08 PM GMT+02:00, Jason Merrill wrote:
> >On Mon, Jul 1, 2019 at 8:59 PM Paul E. McKenney
> >wrote:
> >>
> >> On Tue, Jul 02, 2019 at 05:58:48AM +0530, Akshat Garg wrote:
>
On Tue, Jul 02, 2019 at 02:15:55PM +0100, Ramana Radhakrishnan wrote:
> On Tue, Jul 2, 2019 at 1:38 PM Paul E. McKenney wrote:
>
> >
> > Once a user-created non-dependent pointer is assigned to, it is OK to
> > break the dependency.
>
> Ok, that's good.
>
On Tue, Jul 02, 2019 at 12:01:00PM +0100, Ramana Radhakrishnan wrote:
> >>
> >> It's worth figuring out what passes are doing this - however the worry
> >> I have is that every pass now needs to be handling this case with
> >> respect to pointer attributes. Is there some place that you are
> >> sto
On Tue, Jul 02, 2019 at 05:58:48AM +0530, Akshat Garg wrote:
> On Tue, Jun 25, 2019 at 9:49 PM Akshat Garg wrote:
>
> > On Tue, Jun 25, 2019 at 4:04 PM Ramana Radhakrishnan <
> > ramana@googlemail.com> wrote:
> >
> >> On Tue, Jun 25, 2019 at 11:03 AM Akshat Garg wrote:
> >> >
> >> > As we ha
On Tue, Mar 01, 2016 at 05:55:07PM +0100, Michael Matz wrote:
> Hi,
>
> On Tue, 1 Mar 2016, Richard Biener wrote:
>
> > > What about the example I gave above? Is it unrealistic for compilers
> > > do ever do something like this, or is it just unlikely to gain much
> > > performance, or is it j
On Mon, Feb 29, 2016 at 07:17:55PM +0100, Michael Matz wrote:
> Hi,
>
> On Sat, 27 Feb 2016, Paul E. McKenney wrote:
>
> > But we do already have something very similar with signed integer
> > overflow. If the compiler can see a way to generate faster code that
> >
On Sat, Feb 27, 2016 at 11:16:51AM -0800, Linus Torvalds wrote:
> On Feb 27, 2016 09:06, "Paul E. McKenney"
> wrote:
> >
> >
> > But we do already have something very similar with signed integer
> > overflow. If the compiler can see a way to generate
is
to define a subset of operations where dependencies will be carried.
Note that P0190R0 does call out comparisons as potentially unsafe.
Thanx, Paul
> On Sat, Feb 20, 2016 at 11:53 AM, Paul E. McKenney <
> paul...@linux.vnet.ibm.com> wrote:
>
>
On Fri, Feb 26, 2016 at 11:49:29AM +0100, Richard Biener wrote:
> On Thu, Feb 25, 2016 at 6:33 PM, Torvald Riegel wrote:
> > On Wed, 2016-02-24 at 13:14 +0100, Richard Biener wrote:
> >> On Tue, Feb 23, 2016 at 8:38 PM, Torvald Riegel wrote:
> >> > I'd like to know, based on the GCC experience, h
erry portable Babbage Device
> Original Message
> From: Paul E. McKenney
> Sent: Thursday, February 18, 2016 4:58 AM
> To: paral...@lists.isocpp.org; linux-ker...@vger.kernel.org;
> linux-a...@vger.kernel.org; gcc@gcc.gnu.org; llvm-...@lists.llvm.org
> Reply To: paral...@lists
worried about exactly what sort of marking we use,
but I am convinced that marking is required.
So, given that we need to mark things, what sort of marking would work
best from your perspective?
Thanx, Paul
> On Tue, Sep 22, 2015 at 10
On Mon, Jul 13, 2015 at 05:44:59PM -0700, Paul E. McKenney wrote:
> On Tue, May 19, 2015 at 05:55:10PM -0700, Paul E. McKenney wrote:
> > Hello!
> >
> > Following up on last year's discussion (https://lwn.net/Articles/586838/,
> > https://lwn.net/Articles/58
On Tue, May 19, 2015 at 05:55:10PM -0700, Paul E. McKenney wrote:
> Hello!
>
> Following up on last year's discussion (https://lwn.net/Articles/586838/,
> https://lwn.net/Articles/588300/), I believe that we have a solution. If
> I am wrong, I am sure you all will let m
On Tue, May 26, 2015 at 07:08:35PM +0200, Torvald Riegel wrote:
> On Tue, 2015-05-19 at 17:55 -0700, Paul E. McKenney wrote:
> > http://www.rdrop.com/users/paulmck/RCU/consume.2015.05.18a.pdf
>
> I have been discussing Section 7.9 with Paul during last week.
>
> While I
On Fri, May 22, 2015 at 06:30:29PM +0100, Will Deacon wrote:
> Hi Paul,
>
> On Thu, May 21, 2015 at 09:02:12PM +0100, Paul E. McKenney wrote:
> > On Thu, May 21, 2015 at 08:24:22PM +0100, Will Deacon wrote:
> > > On Wed, May 20, 2015 at 07:16:06PM +0100, Paul E. McKenney
On Fri, May 22, 2015 at 08:43:44AM +0200, Ingo Molnar wrote:
>
> * Linus Torvalds wrote:
>
> > (a) the "official" rules are completely pointless, and make sense
> > only because the standard is written for some random "abstract
> > machine" that doesn't actually exist.
>
> Presuming the inte
On Fri, May 22, 2015 at 06:43:32AM -0400, Richard Kenner wrote:
> > (Assuming it's a goal of this standard to be human parseable to more
> > than a few dozen people on the planet.)
>
> Unfortunately, that's rarely a goal of most standards. ;-)
My experience does match Richard's, sad to say. The
On Thu, May 21, 2015 at 01:42:11PM -0700, Linus Torvalds wrote:
> On Thu, May 21, 2015 at 1:02 PM, Paul E. McKenney
> wrote:
> >
> > The compiler can (and does) speculate non-atomic non-volatile writes
> > in some cases, but I do not believe that it is permitted to specu
On Thu, May 21, 2015 at 08:24:22PM +0100, Will Deacon wrote:
> On Wed, May 20, 2015 at 07:16:06PM +0100, Paul E. McKenney wrote:
> > On Wed, May 20, 2015 at 04:46:17PM +0100, Will Deacon wrote:
> > > On Wed, May 20, 2015 at 01:15:22PM +0100, Paul E. McKenney wrote:
> > &g
On Thu, May 21, 2015 at 06:17:43PM +0200, Michael Matz wrote:
> Hi,
>
> On Thu, 21 May 2015, Paul E. McKenney wrote:
>
> > The point is -exactly- to codify the current state of affairs.
>
> Ah, I see, so it's not yet about creating a more useful (for compilers,
On Thu, May 21, 2015 at 04:22:38PM +0200, Michael Matz wrote:
> Hi,
>
> On Wed, 20 May 2015, Paul E. McKenney wrote:
>
> > > > I'm not sure... you'd require the compiler to perform static analysis of
> > > > loops to determine the state of the
On Wed, May 20, 2015 at 04:54:51PM +0100, Andrew Haley wrote:
> On 05/20/2015 04:46 PM, Will Deacon wrote:
> > I'm not sure... you'd require the compiler to perform static analysis of
> > loops to determine the state of the machine when they exit (if they exit!)
> > in order to show whether or not
On Wed, May 20, 2015 at 04:46:17PM +0100, Will Deacon wrote:
> On Wed, May 20, 2015 at 01:15:22PM +0100, Paul E. McKenney wrote:
> > On Wed, May 20, 2015 at 12:47:45PM +0100, Will Deacon wrote:
> > > On Wed, May 20, 2015 at 03:41:48AM +0100, Paul E. McKenney wrote:
> > >
On Wed, May 20, 2015 at 03:15:48PM +0100, Ramana Radhakrishnan wrote:
>
>
> On 20/05/15 15:03, Paul E. McKenney wrote:
> >On Wed, May 20, 2015 at 02:44:30PM +0100, Ramana Radhakrishnan wrote:
> >>
> >>
> >>On 20/05/15 14:37, David Howells wrote:
>
On Wed, May 20, 2015 at 02:44:30PM +0100, Ramana Radhakrishnan wrote:
>
>
> On 20/05/15 14:37, David Howells wrote:
> >Paul E. McKenney wrote:
> >
> >>I was thinking of "y" as a simple variable, but if it is something more
> >>complex, then the
On Wed, May 20, 2015 at 02:37:05PM +0100, David Howells wrote:
> Paul E. McKenney wrote:
>
> > I was thinking of "y" as a simple variable, but if it is something more
> > complex, then the compiler could do this, right?
> >
> > char *x;
> >
&
On Wed, May 20, 2015 at 02:18:37PM +0100, David Howells wrote:
> Paul E. McKenney wrote:
>
> > > Additionally, what about the following code?
> > >
> > > char *x = y ? z : z;
> > >
> > > Does that extend a dependency chain from z to x
On Wed, May 20, 2015 at 12:47:45PM +0100, Will Deacon wrote:
> Hi Paul,
>
> On Wed, May 20, 2015 at 03:41:48AM +0100, Paul E. McKenney wrote:
> > On Tue, May 19, 2015 at 07:10:12PM -0700, Linus Torvalds wrote:
> > > On Tue, May 19, 2015 at 6:57 PM, Linus Torvalds
> &
On Wed, May 20, 2015 at 11:03:00AM +0200, Richard Biener wrote:
> On Wed, May 20, 2015 at 9:34 AM, Jens Maurer wrote:
> > On 05/20/2015 04:34 AM, Paul E. McKenney wrote:
> >> On Tue, May 19, 2015 at 06:57:02PM -0700, Linus Torvalds wrote:
> >
> >>> - the &
On Wed, May 20, 2015 at 09:34:10AM +0200, Jens Maurer wrote:
> On 05/20/2015 04:34 AM, Paul E. McKenney wrote:
> > On Tue, May 19, 2015 at 06:57:02PM -0700, Linus Torvalds wrote:
>
> >> - the "you can add/subtract integral values" still opens you up to
> >>
On Tue, May 19, 2015 at 07:10:12PM -0700, Linus Torvalds wrote:
> On Tue, May 19, 2015 at 6:57 PM, Linus Torvalds
> wrote:
> >
> > - the "you can add/subtract integral values" still opens you up to
> > language lawyers claiming "(char *)ptr - (intptr_t)ptr" preserving the
> > dependency, which it
On Tue, May 19, 2015 at 06:57:02PM -0700, Linus Torvalds wrote:
> On Tue, May 19, 2015 at 5:55 PM, Paul E. McKenney
> wrote:
> >
> > http://www.rdrop.com/users/paulmck/RCU/consume.2015.05.18a.pdf
>
> >From a very quick read-through, the restricted dependency
Hello!
Following up on last year's discussion (https://lwn.net/Articles/586838/,
https://lwn.net/Articles/588300/), I believe that we have a solution. If
I am wrong, I am sure you all will let me know, and in great detail. ;-)
The key simplification is to "just say no" to RCU-protected array in
On Fri, Mar 07, 2014 at 07:33:25PM +0100, Torvald Riegel wrote:
> On Wed, 2014-03-05 at 10:15 -0800, Paul E. McKenney wrote:
> > On Wed, Mar 05, 2014 at 05:54:59PM +0100, Torvald Riegel wrote:
> > > On Tue, 2014-03-04 at 13:35 -0800, Paul E. McKenney wrote:
> > > >
On Fri, Mar 07, 2014 at 06:45:57PM +0100, Torvald Riegel wrote:
> xagsmtp5.20140307174618.3...@vmsdvm6.vnet.ibm.com
> X-Xagent-Gateway: vmsdvm6.vnet.ibm.com (XAGSMTP5 at VMSDVM6)
>
> On Wed, 2014-03-05 at 10:01 -0800, Paul E. McKenney wrote:
> > On Wed, Mar 05, 2014 at 05:26:3
On Wed, Mar 05, 2014 at 05:54:59PM +0100, Torvald Riegel wrote:
> On Tue, 2014-03-04 at 13:35 -0800, Paul E. McKenney wrote:
> > On Tue, Mar 04, 2014 at 11:00:32AM -0800, Paul E. McKenney wrote:
> > > On Mon, Mar 03, 2014 at 09:46:19PM +0100, Torvald Riegel wrote:
> > >
On Wed, Mar 05, 2014 at 05:26:36PM +0100, Torvald Riegel wrote:
> xagsmtp3.20140305162928.8...@uk1vsc.vnet.ibm.com
> X-Xagent-Gateway: uk1vsc.vnet.ibm.com (XAGSMTP3 at UK1VSC)
>
> On Tue, 2014-03-04 at 11:00 -0800, Paul E. McKenney wrote:
> > On Mon, Mar 03, 2014 at 09:46:1
On Tue, Mar 04, 2014 at 11:00:32AM -0800, Paul E. McKenney wrote:
> On Mon, Mar 03, 2014 at 09:46:19PM +0100, Torvald Riegel wrote:
> > xagsmtp2.20140303204700.3...@vmsdvma.vnet.ibm.com
> > X-Xagent-Gateway: vmsdvma.vnet.ibm.com (XAGSMTP2 at VMSDVMA)
> >
> > On Mon
On Mon, Mar 03, 2014 at 09:46:19PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140303204700.3...@vmsdvma.vnet.ibm.com
> X-Xagent-Gateway: vmsdvma.vnet.ibm.com (XAGSMTP2 at VMSDVMA)
>
> On Mon, 2014-03-03 at 11:20 -0800, Paul E. McKenney wrote:
> > On Mon, Mar 03, 2014 at 07:55:0
On Mon, Mar 03, 2014 at 07:55:08PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140303190831.9...@uk1vsc.vnet.ibm.com
> X-Xagent-Gateway: uk1vsc.vnet.ibm.com (XAGSMTP2 at UK1VSC)
>
> On Fri, 2014-02-28 at 16:50 -0800, Paul E. McKenney wrote:
> > +o Do not use the results from th
On Sun, Mar 02, 2014 at 11:44:52PM +, Peter Sewell wrote:
> On 2 March 2014 23:20, Paul E. McKenney wrote:
> > On Sun, Mar 02, 2014 at 04:05:52AM -0600, Peter Sewell wrote:
> >> On 1 March 2014 08:03, Paul E. McKenney wrote:
> >> > On Sat, Mar 01, 2014 at 04:06:
On Sun, Mar 02, 2014 at 04:05:52AM -0600, Peter Sewell wrote:
> On 1 March 2014 08:03, Paul E. McKenney wrote:
> > On Sat, Mar 01, 2014 at 04:06:34AM -0600, Peter Sewell wrote:
> >> Hi Paul,
> >>
> >> On 28 February 2014 18:50, Paul E. McKenney
> >>
On Sat, Mar 01, 2014 at 04:06:34AM -0600, Peter Sewell wrote:
> Hi Paul,
>
> On 28 February 2014 18:50, Paul E. McKenney
> wrote:
> > On Thu, Feb 27, 2014 at 12:53:12PM -0800, Paul E. McKenney wrote:
> >> On Thu, Feb 27, 2014 at 11:47:08AM -0800, Linus Torvalds w
On Thu, Feb 27, 2014 at 12:53:12PM -0800, Paul E. McKenney wrote:
> On Thu, Feb 27, 2014 at 11:47:08AM -0800, Linus Torvalds wrote:
> > On Thu, Feb 27, 2014 at 11:06 AM, Paul E. McKenney
> > wrote:
> > >
> > > 3. The comparison was against another RCU-prote
On Thu, Feb 27, 2014 at 09:50:21AM -0800, Paul E. McKenney wrote:
> On Thu, Feb 27, 2014 at 04:37:33PM +0100, Torvald Riegel wrote:
> > xagsmtp2.20140227154925.3...@vmsdvm9.vnet.ibm.com
> >
> > On Mon, 2014-02-24 at 11:54 -0800, Linus Torvalds wrote:
> > > On Mon, Fe
On Thu, Feb 27, 2014 at 11:47:08AM -0800, Linus Torvalds wrote:
> On Thu, Feb 27, 2014 at 11:06 AM, Paul E. McKenney
> wrote:
> >
> > 3. The comparison was against another RCU-protected pointer,
> > where that other pointer was properly fetched using on
On Thu, Feb 27, 2014 at 09:50:21AM -0800, Paul E. McKenney wrote:
> On Thu, Feb 27, 2014 at 04:37:33PM +0100, Torvald Riegel wrote:
> > xagsmtp2.20140227154925.3...@vmsdvm9.vnet.ibm.com
> >
> > On Mon, 2014-02-24 at 11:54 -0800, Linus Torvalds wrote:
> > > On Mon, Fe
On Thu, Feb 27, 2014 at 09:01:40AM -0800, Linus Torvalds wrote:
> On Thu, Feb 27, 2014 at 7:37 AM, Torvald Riegel wrote:
> >
> > I agree that just considering syntactic properties of the program seems
> > to be insufficient. Making it instead depend on whether there is a
> > "semantic" dependency
On Thu, Feb 27, 2014 at 04:37:33PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140227154925.3...@vmsdvm9.vnet.ibm.com
>
> On Mon, 2014-02-24 at 11:54 -0800, Linus Torvalds wrote:
> > On Mon, Feb 24, 2014 at 10:53 AM, Paul E. McKenney
> > wrote:
> > >
> > >
On Wed, Feb 26, 2014 at 02:04:30PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140226130517.3...@vmsdvma.vnet.ibm.com
> X-Xagent-Gateway: vmsdvma.vnet.ibm.com (XAGSMTP2 at VMSDVMA)
>
> On Fri, 2014-02-21 at 11:13 -0800, Paul E. McKenney wrote:
> > On Fri, Feb 21, 2014 at 07:35:3
On Tue, Feb 25, 2014 at 10:06:53PM -0500, George Spelvin wrote:
> wrote:
> > wrote:
> >> I have for the last several years been 100% convinced that the Intel
> >> memory ordering is the right thing, and that people who like weak
> >> memory ordering are wrong and should try to avoid reproducing i
On Tue, Feb 25, 2014 at 08:32:38PM -0700, Jeff Law wrote:
> On 02/25/14 17:15, Paul E. McKenney wrote:
> >>I have for the last several years been 100% convinced that the Intel
> >>memory ordering is the right thing, and that people who like weak
> >>memory orderi
On Tue, Feb 25, 2014 at 05:47:03PM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 10:00 PM, Paul E. McKenney
> wrote:
> >
> > So let me see if I understand your reasoning. My best guess is that it
> > goes something like this:
> >
> > 1. The Li
On Mon, Feb 24, 2014 at 10:05:52PM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 3:35 PM, Linus Torvalds
> wrote:
> >
> > Litmus test 1:
> >
> > p = atomic_read(pp, consume);
> > if (p == &variable)
> > return p->val;
> >
> >is *NOT* ordered
>
> Btw, don't get me wron
On Mon, Feb 24, 2014 at 03:35:04PM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 2:37 PM, Paul E. McKenney
> wrote:
> >>
> >> What if the "nothing modifies 'p'" part looks like this:
> >>
> >> if (p != &myvariable)
>
On Mon, Feb 24, 2014 at 11:54:46AM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 10:53 AM, Paul E. McKenney
> wrote:
> >
> > Good points. How about the following replacements?
> >
> > 3. Adding or subtracting an integer to/from a chained pointer
On Mon, Feb 24, 2014 at 10:14:01AM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 9:21 AM, Paul E. McKenney
> wrote:
> >
> > 4. Bitwise operators ("&", "|", "^", and I suppose also "~")
> > applied to a c
On Mon, Feb 24, 2014 at 09:38:46AM -0800, Linus Torvalds wrote:
> On Mon, Feb 24, 2014 at 8:55 AM, Michael Matz wrote:
> >
> > So, let me try to poke holes into your definition or increase my
> > understanding :) . You said "chain of pointers"(dereferences I assume),
> > e.g. if p is result of co
On Mon, Feb 24, 2014 at 09:28:56AM -0800, Paul E. McKenney wrote:
> On Mon, Feb 24, 2014 at 05:55:50PM +0100, Michael Matz wrote:
> > Hi,
> >
> > On Mon, 24 Feb 2014, Linus Torvalds wrote:
> >
> > > > To me that reads like
> > > >
> > &
On Mon, Feb 24, 2014 at 02:55:07PM +0100, Michael Matz wrote:
> Hi,
>
> On Fri, 21 Feb 2014, Paul E. McKenney wrote:
>
> > > And with conservative I mean "everything is a source of a dependency, and
> > > hence can't be removed, reordered or otherwise
On Mon, Feb 24, 2014 at 05:55:50PM +0100, Michael Matz wrote:
> Hi,
>
> On Mon, 24 Feb 2014, Linus Torvalds wrote:
>
> > > To me that reads like
> > >
> > > int i;
> > > int *q = &i;
> > > int **p = &q;
> > >
> > > atomic_XXX (p, CONSUME);
> > >
> > > orders against accesses '*p', '**p',
On Mon, Feb 24, 2014 at 07:57:24AM -0800, Linus Torvalds wrote:
> On Sun, Feb 23, 2014 at 11:31 AM, Linus Torvalds
> wrote:
> >
> > Let me think about it some more, but my gut feel is that just tweaking
> > the definition of what "ordered" means is sufficient.
> >
> > So to go back to the suggeste
On Sun, Feb 23, 2014 at 05:35:28PM -0800, Linus Torvalds wrote:
> On Sun, Feb 23, 2014 at 5:16 PM, Paul E. McKenney
> wrote:
> >>
> >> (a) we've said 'q' is restricted, so there is no aliasing between q
> >> and the pointers b/c. So the compiler i
On Sun, Feb 23, 2014 at 11:31:25AM -0800, Linus Torvalds wrote:
> On Sat, Feb 22, 2014 at 10:34 PM, Paul E. McKenney
> wrote:
> >
> > Adding and subtracting integers to/from a RCU-protected pointer makes
> > sense to me.
>
> Ack. And that's normal "ac
On Sat, Feb 22, 2014 at 07:50:35PM -0800, Linus Torvalds wrote:
> On Sat, Feb 22, 2014 at 4:39 PM, Paul E. McKenney
> wrote:
> >
> > Agreed, by far the most frequent use is "->" to dereference and assignment
> > to store into a local variable. The other op
On Sat, Feb 22, 2014 at 01:53:30PM -0800, Linus Torvalds wrote:
> On Sat, Feb 22, 2014 at 10:53 AM, Torvald Riegel wrote:
> >
> > Stating that (1) "the standard is wrong" and (2) that you think that
> > mo_consume semantics are not good is two different things.
>
> I do agree. They are two indepe
On Sat, Feb 22, 2014 at 07:30:37PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140222183231.5...@emeavsc.vnet.ibm.com
> X-Xagent-Gateway: emeavsc.vnet.ibm.com (XAGSMTP2 at EMEAVSC)
>
> On Thu, 2014-02-20 at 10:18 -0800, Paul E. McKenney wrote:
> > On Thu, Feb 20, 2014 at 06:26:0
On Fri, Feb 21, 2014 at 10:10:54PM +, Joseph S. Myers wrote:
> On Fri, 21 Feb 2014, Paul E. McKenney wrote:
>
> > This needs to be as follows:
> >
> > [[carries_dependency]] int getzero(int i [[carries_dependency]])
> > {
> > return i - i;
> > }
On Fri, Feb 21, 2014 at 06:28:05PM +, Peter Sewell wrote:
> On 20 February 2014 17:01, Linus Torvalds >wrote:
[ . . . ]
> > > So, if you make one of two changes to your example, then I will agree
> > > with you.
> >
> > No. We're not playing games here. I'm fed up with complex examples
> > t
On Fri, Feb 21, 2014 at 07:35:37PM +0100, Michael Matz wrote:
> Hi,
>
> On Thu, 20 Feb 2014, Linus Torvalds wrote:
>
> > But I'm pretty sure that any compiler guy must *hate* that current odd
> > dependency-generation part, and if I was a gcc person, seeing that
> > bugzilla entry Torvald pointed
On Thu, Feb 20, 2014 at 11:45:29AM -0800, Linus Torvalds wrote:
> On Thu, Feb 20, 2014 at 10:56 AM, Paul E. McKenney
> wrote:
> >
> > The example gcc breakage was something like this:
> >
> > i = atomic_load(idx, memory_order_consume);
> > x
On Thu, Feb 20, 2014 at 07:44:32PM +0100, Torvald Riegel wrote:
> xagsmtp3.20140220184514.1...@bldgate.vnet.ibm.com
> X-Xagent-Gateway: bldgate.vnet.ibm.com (XAGSMTP3 at BLDGATE)
>
> On Thu, 2014-02-20 at 10:11 -0800, Paul E. McKenney wrote:
> > But yes, the compiler guys would
On Thu, Feb 20, 2014 at 10:32:51AM -0800, Linus Torvalds wrote:
> On Thu, Feb 20, 2014 at 10:11 AM, Paul E. McKenney
> wrote:
> >
> > You really need that "consume" to be "acquire".
>
> So I think we now all agree that that is what the standard is sa
On Thu, Feb 20, 2014 at 09:34:57AM -0800, Linus Torvalds wrote:
> On Thu, Feb 20, 2014 at 9:14 AM, Torvald Riegel wrote:
> >>
> >> So the clarification is basically to the statement that the "if
> >> (consume(p)) a" version *would* have an ordering guarantee between the
> >> read of "p" and "a", b
On Thu, Feb 20, 2014 at 06:54:06PM +0100, Torvald Riegel wrote:
> xagsmtp4.20140220175519.1...@vmsdvm6.vnet.ibm.com
> X-Xagent-Gateway: vmsdvm6.vnet.ibm.com (XAGSMTP4 at VMSDVM6)
>
> On Thu, 2014-02-20 at 00:30 -0800, Paul E. McKenney wrote:
> > Well, all the compilers current
On Thu, Feb 20, 2014 at 06:26:08PM +0100, Torvald Riegel wrote:
> xagsmtp2.20140220172700.0...@vmsdvm4.vnet.ibm.com
> X-Xagent-Gateway: vmsdvm4.vnet.ibm.com (XAGSMTP2 at VMSDVM4)
>
> On Wed, 2014-02-19 at 20:01 -0800, Paul E. McKenney wrote:
> > On Wed, Feb 19, 2014 at 04:53
On Thu, Feb 20, 2014 at 09:01:06AM -0800, Linus Torvalds wrote:
> On Thu, Feb 20, 2014 at 12:30 AM, Paul E. McKenney
> wrote:
> >>
> >> So lets make this really simple: if you have a consume->cmp->read, is
> >> the ordering of the two reads guaranteed?
>
On Thu, Feb 20, 2014 at 12:30:32AM -0800, Paul E. McKenney wrote:
> On Wed, Feb 19, 2014 at 08:43:14PM -0800, Linus Torvalds wrote:
[ . . . ]
> So, if you make one of two changes to your example, then I will agree
> with you. The first change is to have a real data dependency between
&
On Wed, Feb 19, 2014 at 08:43:14PM -0800, Linus Torvalds wrote:
> On Wed, Feb 19, 2014 at 8:01 PM, Paul E. McKenney
> wrote:
> >
> > The control dependency should order subsequent stores, at least assuming
> > that "a" and "b" don't start off with
On Wed, Feb 19, 2014 at 04:53:49PM -0800, Linus Torvalds wrote:
> On Tue, Feb 18, 2014 at 11:47 AM, Torvald Riegel wrote:
> > On Tue, 2014-02-18 at 09:44 -0800, Linus Torvalds wrote:
> >>
> >> Can you point to it? Because I can find a draft standard, and it sure
> >> as hell does *not* contain any
On Wed, Feb 19, 2014 at 06:55:51PM +0100, Torvald Riegel wrote:
> On Wed, 2014-02-19 at 07:14 -0800, Paul E. McKenney wrote:
> > On Wed, Feb 19, 2014 at 11:59:08AM +0100, Torvald Riegel wrote:
[ . . . ]
> > > On both sides, the compiler will see that mmap() (or similar) is cal
On Wed, Feb 19, 2014 at 11:59:08AM +0100, Torvald Riegel wrote:
> On Tue, 2014-02-18 at 14:58 -0800, Paul E. McKenney wrote:
> > On Tue, Feb 18, 2014 at 10:40:15PM +0100, Torvald Riegel wrote:
> > > xagsmtp4.20140218214207.8...@vmsdvm9.vnet.ibm.com
> > > X-Xagent-Ga
On Tue, Feb 18, 2014 at 10:40:15PM +0100, Torvald Riegel wrote:
> xagsmtp4.20140218214207.8...@vmsdvm9.vnet.ibm.com
> X-Xagent-Gateway: vmsdvm9.vnet.ibm.com (XAGSMTP4 at VMSDVM9)
>
> On Tue, 2014-02-18 at 09:16 -0800, Paul E. McKenney wrote:
> > On Tue, Feb 18, 2014 at 08:49
On Tue, Feb 18, 2014 at 09:43:31PM +0100, Torvald Riegel wrote:
> xagsmtp5.20140218204423.3...@bldgate.vnet.ibm.com
> X-Xagent-Gateway: bldgate.vnet.ibm.com (XAGSMTP5 at BLDGATE)
>
> On Tue, 2014-02-18 at 12:12 +, Peter Sewell wrote:
> > Several of you have said that the standard and compiler
On Tue, Feb 18, 2014 at 10:49:27AM -0800, Linus Torvalds wrote:
> On Tue, Feb 18, 2014 at 10:21 AM, Peter Sewell
> wrote:
> >
> > This is a bit more subtle, because (on ARM and POWER) removing the
> > dependency and conditional branch is actually in general *not* equivalent
> > in the hardware, in
On Tue, Feb 18, 2014 at 06:23:47PM +, Peter Sewell wrote:
> On 18 February 2014 17:16, Paul E. McKenney
> wrote:
> > On Tue, Feb 18, 2014 at 08:49:13AM -0800, Linus Torvalds wrote:
> >> On Tue, Feb 18, 2014 at 7:31 AM, Torvald Riegel wrote:
> >> > On Mon,
On Tue, Feb 18, 2014 at 09:44:48AM -0800, Linus Torvalds wrote:
> On Tue, Feb 18, 2014 at 8:17 AM, Torvald Riegel wrote:
[ . . . ]
> > The standard is clear on what's required. I strongly suggest reading
> > the formalization of the memory model by Batty et al.
>
> Can you point to it? Because
On Tue, Feb 18, 2014 at 03:16:33PM +, Mark Batty wrote:
> Hi Paul,
>
> Thanks for the document. I'm looking forward to reading the bits about
> dependency chains in Linux.
And I am looking forward to your thoughts on those bits!
> > One point of confusion for me... Example 4 says "language
On Tue, Feb 18, 2014 at 08:49:13AM -0800, Linus Torvalds wrote:
> On Tue, Feb 18, 2014 at 7:31 AM, Torvald Riegel wrote:
> > On Mon, 2014-02-17 at 16:05 -0800, Linus Torvalds wrote:
> >> And exactly because I know enough, I would *really* like atomics to be
> >> well-defined, and have very clear -
On Tue, Feb 18, 2014 at 04:38:40PM +0100, Torvald Riegel wrote:
> On Mon, 2014-02-17 at 16:18 -0800, Linus Torvalds wrote:
> > On Mon, Feb 17, 2014 at 3:41 PM, Torvald Riegel wrote:
> > >
> > > There's an underlying problem here that's independent from the actual
> > > instance that you're worried
On Tue, Feb 18, 2014 at 04:56:40PM +0100, Torvald Riegel wrote:
> On Mon, 2014-02-17 at 19:00 -0800, Paul E. McKenney wrote:
> > On Mon, Feb 17, 2014 at 12:18:21PM -0800, Linus Torvalds wrote:
> > > On Mon, Feb 17, 2014 at 11:55 AM, Torvald Riegel
> > > wrote:
>
On Tue, Feb 18, 2014 at 03:33:35PM +, Peter Sewell wrote:
> Hi Paul,
>
> On 18 February 2014 14:56, Paul E. McKenney
> wrote:
> > On Tue, Feb 18, 2014 at 12:12:06PM +, Peter Sewell wrote:
> >> Several of you have said that the standard and compiler should
On Tue, Feb 18, 2014 at 12:12:06PM +, Peter Sewell wrote:
> Several of you have said that the standard and compiler should not
> permit speculative writes of atomics, or (effectively) that the
> compiler should preserve dependencies. In simple examples it's easy
> to see what that means, but i
On Mon, Feb 17, 2014 at 07:42:42PM -0800, Linus Torvalds wrote:
> On Mon, Feb 17, 2014 at 7:24 PM, Linus Torvalds
> wrote:
> >
> > As far as I can tell, the intent is that you can't do value
> > speculation (except perhaps for the "relaxed", which quite frankly
> > sounds largely useless).
>
> Hm
On Mon, Feb 17, 2014 at 07:24:56PM -0800, Linus Torvalds wrote:
> On Mon, Feb 17, 2014 at 7:00 PM, Paul E. McKenney
> wrote:
> >
> > One example that I learned about last week uses the branch-prediction
> > hardware to validate value speculation. And no, I am not a
On Mon, Feb 17, 2014 at 12:18:21PM -0800, Linus Torvalds wrote:
> On Mon, Feb 17, 2014 at 11:55 AM, Torvald Riegel wrote:
> >
> > Which example do you have in mind here? Haven't we resolved all the
> > debated examples, or did I miss any?
>
> Well, Paul seems to still think that the standard pos
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