linux-kernel - Dynticks on Vortex86SX ? (Cx486SLC + just the standard i8254 PC timer)

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Message-ID: <4B86EF85.12688.440738@Frantisek.Rysanek.post.cz>
Date:	Thu, 25 Feb 2010 21:45:41 +0100
From:	"Frantisek Rysanek" <Frantisek.Rysanek@...t.cz>
To:	linux-kernel@...r.kernel.org
Subject: Dynticks on Vortex86SX ? (Cx486SLC + just the standard i8254 PC timer)

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

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 :-)

Frank Rysanek

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