m4/clock_time.m4 from r117596

m4/clock_time.m4 from r117596

[Dmitry Antipov]

IIUC this should be incorporated into gnulib.

Dmitry

Re: m4/clock_time.m4 from r117596

[Paul Eggert]

Dmitry Antipov wrote:
> IIUC this should be incorporated into gnulib.

Thanks for the heads-up, but isn't that change unnecessary? 
timer_settime and timerfd_settime already round clocks up to the nearest 
value supported by the system resolution, so there should be no need for 
Emacs to call clock_getres and round the clocks by hand.

I gave that a shot, and simplified some other parts of the recent atimer 
changes, in trunk bzr 117616.

Re: m4/clock_time.m4 from r117596

[Dmitry Antipov]

On 08/01/2014 12:19 AM, Paul Eggert wrote:

> timer_settime and timerfd_settime already round clocks up to the nearest
> value supported by the system resolution

Are you sure about that?  On my (Fedora 20) system, 'man timer_settime' and
'man timerfd_settime' says nothing about resolution and rounding.  But 'man
clock_settime' says:

"If the time value pointed to by the argument tp of clock_settime() is not
a multiple of res, then it is _truncated_ to a multiple of res."

Dmitry

Re: m4/clock_time.m4 from r117596

[Paul Eggert]

Dmitry Antipov wrote:
> Are you sure about that?  On my (Fedora 20) system, 'man timer_settime' and
> 'man timerfd_settime' says nothing about resolution and rounding.

It's a POSIX requirement for timer_settime, and I expect timerfd_settime 
to be similar.  I'd be surprised if the Linux kernel did it any differently.

A bit of reflection should make it clear why this is so (and why 
clock_settime is different): an application must always allow for the 
act of computation to advance the clock a little bit, so if the system 
rounds timers up and clocks down it won't hurt apps any more than 
they're hurt already simply by running.

Here's the POSIX requirement:

"Time values that are between two consecutive non-negative integer 
multiples of the resolution of the specified timer shall be rounded up 
to the larger multiple of the resolution."

http://pubs.opengroup.org/onlinepubs/9699919799/functions/timer_settime.html