# Re: \[RFCv4\] timerfd: add TFD\_NOTIFY\_CLOCK\_SET to watch for clock changes

- From: Thomas Gleixner \<hidden\>
- Date: 2011-03-10 09:08:18 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2011/03/51547
- Thread: https://ratatoskr.run/linux-fsdevel/2011/03/51532/t.md

```text
On Thu, 10 Mar 2011, Kay Sievers wrote:

> On Thu, Mar 10, 2011 at 01:25, Andrew Morton [ref] wrote:
> > On Wed,  9 Mar 2011 16:36:51 +0200
> > Alexander Shishkin [ref] wrote:
> >
> >> Changes since v3:
> >>  - changed timerfd_settime() semantics (see below)
> >> Changes since v2:
> >>  - replaced sysfs interface with a syscall
> >>  - added sysctl/procfs handle to set a limit to the number of users
> >>  - fixed issues pointed out by Greg.
> >> Changes since v1:
> >>  - updated against 2.6.36-rc1,
> >>  - added notification/filtering options,
> >>  - added Documentation/ABI/sysfs-kernel-time-notify interface description.
> 
> > It would be helpful to know if the identified users of this feature
> > actually find it useful and adequate.  I guess the most common
> > application is the 1,001 desktop clock widgets.  Do you have any
> > feedback from any of the owners of those?
> 
> We want it for systemd, to provide cron-like functionality but without
> the need to stupidly wake up every minute and check the system time
> for possible jumps.
> 
> It also sounds useful for a generic resume (after system suspend)
> notification for applications, which isn't really possible today.

Note, that we have CLOCK_BOOTTIME pending for .39 which aims at the
same problem. It's basically CLOCK_MONOTONIC adjusted by the time we
were in suspend. So while CLOCK_MONOTONIC timers are not aware of the
time spent in suspend CLOCK_BOOTTIME timers are. The reason for
implementing CLOCK_BOOTTIME was basically the same problem.

Thanks,

	tglx
```