On Fri, Feb 09, 2018 at 06:29:23AM -0800, Paul E. McKenney wrote: > On Fri, Feb 09, 2018 at 01:50:51PM +0100, Andrea Parri wrote: > > On Fri, Feb 09, 2018 at 04:31:00AM -0800, Paul E. McKenney wrote: > > > On Sun, Feb 04, 2018 at 07:37:08PM +0100, Andrea Parri wrote: > > > > Hi Akira, > > > > > > > > On Mon, Feb 05, 2018 at 01:14:10AM +0900, Akira Yokosawa wrote: > > > > > Hi Paul, > > > > > CC: Andrea > > > > > > > > > > This is intentionally off the list, as I was not cc'd in the thread. > > > > > If you think it is worthwhile, could you help me join the thread by > > > > > forwarding the following part as a reply to your message, plus CC: to > > > > > me. > > > > > > > > [CCing lists and other people] > > > > > > > > > > > > > > > > > > On Fri, Feb 02, 2018 at 17:21:03AM -0800, Paul E. McKenney wrote: > > > > > > On Fri, Feb 02, 2018 at 10:12:48AM +0100, Andrea Parri wrote: > > > > > >> Recent efforts led to the specification of a memory consistency > > > > > >> model > > > > > >> for the Linux kernel [1], which "can (roughly speaking) be thought > > > > > >> of > > > > > >> as an automated version of memory-barriers.txt" and which is (in > > > > > >> turn) > > > > > >> "accompanied by extensive documentation on its use and its design". > > > > > >> > > > > > >> Make sure that the (occasional) reader of memory-barriers.txt will > > > > > >> be > > > > > >> aware of these developments. > > > > > >> > > > > > >> [1] https://marc.info/?l=linux-kernel&m=151687290114799&w=2 > > > > > >> > > > > > >> Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx> > > > > > > > > > > > > I am inclined to pull in something along these lines, but would like > > > > > > some feedback on the wording, especially how "official" we want to > > > > > > make the memory model to be. > > > > > > > > > > > > Thoughts? > > > > > > > > > > The change log of commit e7720af5f9ac ("locking/Documentation: Add > > > > > disclaimer") says: > > > > > > > > > > It appears people are reading this document as a requirements > > > > > list for > > > > > building hardware. This is not the intent of this document. Nor > > > > > is it > > > > > particularly suited for this purpose. > > > > > > > > > > The primary purpose of this document is our collective attempt to > > > > > define > > > > > a set of primitives that (hopefully) allow us to write correct > > > > > code on > > > > > the myriad of SMP platforms Linux supports. > > > > > > > > > > Its a definite work in progress as our understanding of these > > > > > platforms, > > > > > and memory ordering in general, progresses. > > > > > > > > > > Nor does being mentioned in this document mean we think its a > > > > > particularly good idea; the data dependency barrier required by > > > > > Alpha > > > > > being a prime example. Yes we have it, no you're insane to > > > > > require it > > > > > when building new hardware. > > > > > > > > > > My take on the Linux Kernel memory-consistency model is a supplement > > > > > of > > > > > memory-barriers.txt and the disclaimer also applies to the memory > > > > > model. > > > > > > > > > > > > > > > > > If I don't hear otherwise in a couple of days, I will pull this as > > > > > > is. > > > > > > > > > > > > Thanx, Paul > > > > > > > > > > > >> --- > > > > > >> Documentation/memory-barriers.txt | 4 +++- > > > > > >> 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > >> > > > > > >> diff --git a/Documentation/memory-barriers.txt > > > > > >> b/Documentation/memory-barriers.txt > > > > > >> index a863009849a3b..8cc3f098f4a7d 100644 > > > > > >> --- a/Documentation/memory-barriers.txt > > > > > >> +++ b/Documentation/memory-barriers.txt > > > > > >> @@ -17,7 +17,9 @@ meant as a guide to using the various memory > > > > > >> barriers provided by Linux, but > > > > > >> in case of any doubt (and there are many) please ask. > > > > > >> > > > > > >> To repeat, this document is not a specification of what Linux > > > > > >> expects from > > > > > >> -hardware. > > > > > >> +hardware. For such a specification, in the form of a memory > > > > > >> consistency > > > > > >> +model, and for documentation about its usage and its design, the > > > > > >> reader is > > > > > >> +referred to "tools/memory-model/". > > > > > >> > > > > > > > > > > Adding cross-reference in this way can _weaken_ the message of the > > > > > disclaimer. > > > > > > > > Thank you for your remarks; I do share the same concern. > > > > > > > > > What about adding it in the previous sentence as the patch appended > > > > > bellow? > > > > > > > > I do like this idea: I believe that my phrasing (and that "what Linux > > > > expects from hardware") may be easily subject to misinterpretation... > > > > which your solution can avoid. > > > > > > Any objections to Akira's patch below? (Give or take the usual > > > wordsmithing.) > > > > > > Andrea, should I interpret your paragraph above ask an Acked-by? > > > > Well, I am among the Signed-off-by: of the patch; it didn't seem too fair > > to me to Ack my own patch... ;-) Is the wording sound? other suggestions? > > Good point, too many all-day meetings last week. ;-) > > How about the following?
Even better IMO, Thanks! Andrea > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 9370f98c312d658afe88e548d469549d8f31e402 > Author: Andrea Parri <parri.and...@gmail.com> > Date: Fri Feb 9 06:26:08 2018 -0800 > > Documentation/memory-barriers.txt: Cross-reference "tools/memory-model/" > > A memory consistency model is now available for the Linux kernel [1], > which "can (roughly speaking) be thought of as an automated version of > memory-barriers.txt" and which is (in turn) "accompanied by extensive > documentation on its use and its design". > > Inform the (occasional) reader of memory-barriers.txt of these > developments. > > [1] https://marc.info/?l=linux-kernel&m=151687290114799&w=2 > > Co-developed-by: Andrea Parri <parri.and...@gmail.com> > Co-developed-by: Akira Yokosawa <aki...@gmail.com> > Signed-off-by: Andrea Parri <parri.and...@gmail.com> > Signed-off-by: Akira Yokosawa <aki...@gmail.com> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > diff --git a/Documentation/memory-barriers.txt > b/Documentation/memory-barriers.txt > index 479ecec80593..74ad222d11ed 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -14,7 +14,11 @@ DISCLAIMER > This document is not a specification; it is intentionally (for the sake of > brevity) and unintentionally (due to being human) incomplete. This document > is > meant as a guide to using the various memory barriers provided by Linux, but > -in case of any doubt (and there are many) please ask. > +in case of any doubt (and there are many) please ask. Some doubts may be > +resolved by referring to the formal memory consistency model and related > +documentation at tools/memory-model/. Nevertheless, even this memory > +model should be viewed as the collective opinion of its maintainers rather > +than as an infallible oracle. > > To repeat, this document is not a specification of what Linux expects from > hardware. > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
