linux-kernel - Re: Revised futex(2) man page for review

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Date:	Mon, 27 Jul 2015 13:00:50 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Davidlohr Bueso <dave@...olabs.net>,
	Peter Zijlstra <peterz@...radead.org>
CC:	mtk.manpages@...il.com, Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	Carlos O'Donell <carlos@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux API <linux-api@...r.kernel.org>,
	Torvald Riegel <triegel@...hat.com>,
	Roland McGrath <roland@...k.frob.com>,
	Darren Hart <dvhart@...radead.org>,
	Anton Blanchard <anton@...ba.org>,
	Eric Dumazet <edumazet@...gle.com>,
	bill o gallmeister <bgallmeister@...il.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Daniel Wagner <wagi@...om.org>, Rich Felker <dalias@...c.org>,
	Andy Lutomirski <luto@...capital.net>,
	bert hubert <bert.hubert@...herlabs.nl>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Heinrich Schuchardt <xypron.glpk@....de>
Subject: Re: Revised futex(2) man page for review

Hi David,

On 03/31/2015 10:36 PM, Davidlohr Bueso wrote:
> On Sat, 2015-03-28 at 13:03 +0100, Peter Zijlstra wrote:
>>>               If the timeout argument is non-NULL, its contents specify a rel‐
>>>               ative   timeout   for   the  wait,  measured  according  to  the
>>>               CLOCK_MONOTONIC clock.  (This interval will be rounded up to the
>>>               system clock granularity, and kernel scheduling delays mean that
>>>               the blocking interval may overrun by a small amount.)  If  time‐
>>>               out is NULL, the call blocks indefinitely.
>>
>> Would it not be better to only state that the wait will not return
>> before the timeout -- unless woken -- and not bother with clock
>> granularity and scheduling delays?
> 
> Yeah, similarly we also have this:
> 
>      FUTEX_PRIVATE_FLAG (since Linux 2.6.22)
>               This option bit can be employed with all futex  operations.   It
>               tells  the  kernel  that  the  futex  is process-private and not
>               shared with another process (i.e., it is  only  being  used  for
>               synchronization  between  threads  of  the  same process).  This
>               allows the kernel to choose the fast  path  for  validating  the
>               user-space address and avoids expensive VMA lookups, taking ref‐
>               erence counts on file backing store, and so on.
> 
> This to me reads a bit too much into the kernel (fastpath, refcnt,
> vmas). Why not just mention that it avoids overhead in the kernel or
> something? I don't recall any manpage mentioning such details, but I
> could be wrong. 

Thanks. Agreed. I changed this to

    This allows the kernel to make some additional performance optimizations.

> In any case its a nit, the whole doc is pretty good and
> I hope you can merge it soon and then just increment ;)

I ran out of time and energy at a certain point. And also got a little
disheartened that I got more people complaining about groff markup
than actually looked looked at the FIXMEs in the page source :-). 
I'll try to reboot the process.

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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