[systemd-devel] [EXT] Re: Understanding the effect of AccuracySec=

[Barry]

> On 19 Aug 2024, at 08:38, Andrei Borzenkov <arvidjaar at gmail.com> wrote:
> 
> On Mon, Aug 19, 2024 at 10:11 AM Barry <barry at barrys-emacs.org> wrote:
>> 
>> 
>> 
>> On 19 Aug 2024, at 06:55, Windl, Ulrich <u.windl at ukr.de> wrote:
>> 
>> 
>> Despite of the fact that my version of systemd does not know that setting, can you explain what the effect of AccuracySec= really is?
>> 
>> 
>> The docs https://www.man7.org/linux/man-pages/man5/systemd.timer.5.html say this
>> 
>> Note that this setting is primarily a power saving option
>>           that allows coalescing CPU wake-ups. It should not be
>>           confused with RandomizedDelaySec= (see below) which adds a
>>           random value to the time the timer shall elapse next and
>>           whose purpose is the opposite: to stretch elapsing of timer
>>           events over a longer period to reduce workload spikes. For
>>           further details and explanations and how both settings play
>>           together, see below.
>> 
>> So if you have 5 timers that expire about the same time this allows them to all run at the sane time thus saving power.
> 
> It does explain why timers are run at the same time. It does not
> explain why "daily" + accuracy 6h runs at midnight, not close to 6am

My guess, based on the docs, is that daily can start at midnight and the
accuracy allows it to be delayed till 06:00 if other timers are also in that
windows. If there are no other timers or the others are all daily as well then
midnight is correct.

Barry



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