Re: Revised futex(2) man page for review

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

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/