Re: [EXT] Re: Understanding the effect of AccuracySec=

["Windl, Ulrich" <u.windl@xxxxxx>]

> -----Original Message-----
> From: Andrei Borzenkov <arvidjaar@xxxxxxxxx>
> Sent: Saturday, August 17, 2024 8:22 AM
> To: Windl, Ulrich <u.windl@xxxxxx>; systemd-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: [EXT] Re:  Understanding the effect of
> AccuracySec=
> 
> On 16.08.2024 12:43, Windl, Ulrich wrote:
> > Hi!
> >
> > I have defined a time using
> >
> > [Timer]
> > OnCalendar=daily
> > AccuracySec=6h
> > Persistent=true
> >
> > And the idea was to run the unit daily, but it's rather unimportant when,
> just nout in prime hours.
> >
> > The man page says:
> >
> >         AccuracySec=
> >             Specify the accuracy the timer shall elapse with. Defaults to 1min.
> >             The timer is scheduled to elapse within a time window starting with
> >             the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
> >             OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
> >             the time configured with AccuracySec= later. Within this time
> >             window, the expiry time will be placed at a host-specific,
> >             randomized but stable position that is synchronized between all
> >             local timer units. This is done in order to distribute the wake-up
> >             time in networked installations, as well as optimizing power
> >             consumption to suppress unnecessary CPU wake-ups. To get best
> >             accuracy, set this option to 1us. Note that the timer is still
> >             subject to the timer slack configured via systemd-system.conf(5)'s
> >             TimerSlackNSec= setting. See prctl(2) for details. To optimize
> >             power consumption, make sure to set this value as high as possible
> >             and as low as necessary.
> >
> > So I expected that multiple instances of the timer would be "spread", but
> instead I see all instances started at 00:00:01.
> 
> It sounds like you want RandomizedDelaySec, not AccuracySec.
[Windl, Ulrich] 

Despite of the fact that my version of systemd does not know that setting, can you explain what the effect of AccuracySec= really is?

[...]