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Message-ID: <4b6f1278-9c73-576a-2072-e49622c0a1ee@gmail.com>
Date: Fri, 9 Feb 2018 22:11:24 +0900
From: Akira Yokosawa <akiyks@...il.com>
To: Andrea Parri <parri.andrea@...il.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
stern@...land.harvard.edu, will.deacon@....com,
peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
corbet@....net, Akira Yokosawa <akiyks@...il.com>
Subject: Re: [PATCH 1/2] Documentation/memory-barriers.txt: cross-reference
"tools/memory-model/"
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@...xxxxxx>
>>>>>
>>>>> 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@...il.com>
???
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@...il.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.andrea@...il.com>
>>>> Signed-off-by: Akira Yokosawa <akiyks@...il.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
>>>>
>>>>
>>>>
>>>
>>
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