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SubjectRe: Dynticks on Vortex86SX ? (Cx486SLC + just the standard i8254 PC timer)
Frantisek Rysanek writes:
> Dear Gentlemen,
>
> I'm having fun with a Vortex-based motherboard, under 2.6.33.
> Linux reports the CPU as a Cx486SLC :-)
> A complete PC-compatible motherboard (without VGA) running at ~ 2
> Watts.
> I'm wondering how to decrease the power consumption even further,
> and "tickless" operation comes to mind.
> And that's where I have a problem. Even if I enable
> "Tickless System (Dynamic Ticks)" in the menuconfig,
> there's no apparent change in consumption, and I still get
> around 200-300 timer interrupts per second...
>
> These are some entries from my .config that might be relevant:
>
> CONFIG_TICK_ONESHOT=y
> CONFIG_NO_HZ=y
> # CONFIG_HIGH_RES_TIMERS is not set
> CONFIG_M486=y
> CONFIG_HZ_250=y
> CONFIG_HZ=250

Select HZ=100.

> The only timer that this platform contains (known to Linux)
> is the generic i8254-compatible PC timer.
>
> Makes me wonder if this platform is capable of "tickless" operation
> at all. Or maybe my particular combination of features in the .config
> effectively prevents the long idle periods from occurring?
>
> Apart from a standard init and getty's, there's a dhclient and sshd
> running on the machine... it's a fairly minimal text-mode system.
>
> Any ideas are welcome :-)

Enable CONFIG_DEBUG_KERNEL and CONFIG_TIMER_STATS, rebuild and reboot.
cat /proc/interrupts, echo 1 > /proc/timer_stats, sleep for 10 seconds,
cat /proc/timer_stats and /proc/interrupts.
That'll tell you which timers are firing the most, which translates into
requiring frequent timer interrupts.


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