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. Andrea > > The tag use in the change log may need adjustments. I'm not familiar with the > manner in modifying other persons' patches. Of course, the wording itself can > be improved further. Any feedback is welcome. > > Thanks, Akira > > >> The purpose of this document is twofold: > >> > >> -- > >> 2.7.4 > >> > > ----8<------- > From 714e8c4b09acd6e965de116532dce05070b9e636 Mon Sep 17 00:00:00 2001 > From: Akira Yokosawa <aki...@gmail.com> > Date: Mon, 5 Feb 2018 00:28:36 +0900 > Subject: [PATCH] Documentation/memory-barriers.txt: cross-reference > "tools/memory-model/" > > 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.and...@gmail.com> > Signed-off-by: Akira Yokosawa <aki...@gmail.com> > --- > 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 479ecec..975488d 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -14,7 +14,9 @@ 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. For clarification of > such > +doubt, 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/". > > To repeat, this document is not a specification of what Linux expects from > hardware. > -- > 2.7.4 > > >
