On 2018/02/09 21:50, 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? > > Andrea Well, I should have kept the author of the patch. I.e. I guess the author should have been From: Andrea Parri <parri.andrea@xxxxxxxxx> ??? If you'd like, I can respin the patch. Thanks, Akira > > >> >> Thanx, Paul >> >>> 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 <akiyks@xxxxxxxxx> >>>> 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.andrea@xxxxxxxxx> >>>> Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx> >>>> --- >>>> 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 >>>> >>>> >>>> >>> >> -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
