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Message-ID: <5674FF20.9030609@gmail.com>
Date: Sat, 19 Dec 2015 07:54:24 +0100
From: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To: Torvald Riegel <triegel@...hat.com>
Cc: mtk.manpages@...il.com, Darren Hart <dvhart@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
lkml <linux-kernel@...r.kernel.org>,
libc-alpha <libc-alpha@...rceware.org>,
linux-man <linux-man@...r.kernel.org>,
Carlos O'Donell <carlos@...hat.com>,
Roland McGrath <roland@...k.frob.com>,
Davidlohr Bueso <dave@...olabs.net>,
Jakub Jelinek <jakub@...hat.com>, Ingo Molnar <mingo@...e.hu>,
bill o gallmeister <bgallmeister@...il.com>,
bert hubert <bert.hubert@...herlabs.nl>,
Jan Kiszka <jan.kiszka@...mens.com>,
Eric Dumazet <edumazet@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Rusty Russell <rusty@...tcorp.com.au>,
Heinrich Schuchardt <xypron.glpk@....de>,
Andy Lutomirski <luto@...capital.net>,
Daniel Wagner <wagi@...om.org>,
Anton Blanchard <anton@...ba.org>,
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Rich Felker <dalias@...c.org>,
Jonathan Wakely <jwakely@...hat.com>,
Mike Frysinger <vapier@...too.org>
Subject: Re: futex(3) man page, final draft for pre-release review
On 12/18/2015 12:11 PM, Torvald Riegel wrote:
> On Wed, 2015-12-16 at 16:54 +0100, Michael Kerrisk (man-pages) wrote:
>> Hello Darren,
>>
>> On 12/15/2015 10:18 PM, Darren Hart wrote:
>>> On Tue, Dec 15, 2015 at 02:43:50PM +0100, Michael Kerrisk (man-pages) wrote:
>>
>> [...]
>>
>>>> When executing a futex operation that requests to block a thread,
>>>> the kernel will block only if the futex word has the value that
>>>> the calling thread supplied (as one of the arguments of the
>>>> futex() call) as the expected value of the futex word. The load‐
>>>> ing of the futex word's value, the comparison of that value with
>>>> the expected value, and the actual blocking will happen atomi‐
>>>>
>>>> FIXME: for next line, it would be good to have an explanation of
>>>> "totally ordered" somewhere around here.
>>>>
>>>> cally and totally ordered with respect to concurrently executing
>>>
>>> Totally ordered with respect futex operations refers to semantics of the
>>> ACQUIRE/RELEASE operations and how they impact ordering of memory reads and
>>> writes. The kernel futex operations are protected by spinlocks, which ensure
>>> that that all operations are serialized with respect to one another.
>>>
>>> This is a lot to attempt to define in this document. Perhaps a reference to
>>> linux/Documentation/memory-barriers.txt as a footnote would be sufficient? Or
>>> perhaps for this manual, "serialized" would be sufficient, with a footnote
>>> regarding "totally ordered" and a pointer to the memory-barrier documentation?
>>
>> I think I'll just settle for writing serialized in the man page, and be
>> done with it :-).
>
> I'd prefer if you'd not just use "serialized" :)
Sigh :-). Okay--removed.
> Eventually, I'd prefer
> if we can explain the semantics for the user in terms of the terminology
> and semantics of the memory model of the programming language that users
> will likely use to call futex ops (ie, C11 / C++11).
And I'd be really happy to see such an explanation land in the page.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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