tickless cron

Rogelio Serrano rogelio.serrano at gmail.com
Mon Sep 25 01:39:53 UTC 2006


On 9/25/06, Rich Felker <dalias at aerifal.cx> wrote:
> On Sun, Sep 24, 2006 at 11:52:02PM +0200, Denis Vlasenko wrote:
> > > what i mean is not have cron set a timer to one minute and evaluating
> > > all the schedules once a minute. the present crontab format works well
> > > in that mode becaue its just a straight comparison with the present
> > > time and the values in a crontab line which can actually be placed in
> > > a 'struct time'. what i would like to have is for cron to set the
> > > timer exactly to the next timeout. i have a tickless kernel and it
> > > does not make sense for cron the do exactly what i just removed from
> > > the kernel.
> >
> > Just think what will happen if someone will set system time...
>

the utility for setting system time tells cron that the time changed.
im not using a separate crond actually. i put that functionality in
init and init is talking to a notification server. so when it receives
a system time change notification it recomputes everything.

> It's totally acceptable to wake up once a minute and make sure the
> system time did not change drastically. It's not acceptable to run
> thru the entire crontab every minute for no reason. The overall
> processing time may be low, but the _spike_ in load could be
> problematic. It also prevents the memory used storing the crontab
> entries (or the file if the file is read every time) from getting
> swapped out, which is annoying on low-memory systems.
>

our tests with machines that are accessed about once a week shows 30%
less power consumption with a totally tickless system. on a desktop
accessed frequently it does not make a difference.

> > Periodic check every minute really isn't a load worth optimizing out.
>
> It is for many reasons, not the least of which is that the solution
> with it "optimized out" is actually smaller and simpler too!!
>
> Rich
>
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-- 
the thing i like with my linux pc is that i can sum up my complaints in 5 items



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