Re: dynamic-hz

Russell King
2004-12-13T20:18:45Z

On Mon, Dec 13, 2004 at 04:23:55PM +0000, Russell King wrote:
> There is another twist here though - the Linux kernel kicks itself out
> of idle mode and into some other thread multiple times a second while
> the system is idle. So far, in all my Linux kernel experience, I've
> yet to see a kernel where it's possible to stay in the idle thread
> for more than half a second. (The ARM kernels I run are always
> configured with IDLE LED support, so I can _see_ when it gets kicked
> out of the idle thread.)

For futher information only, analysing this further, we keep switching
to the events/0 thread, and it seems to be mainly for:

- cursor handling every 200ms
- slab cache reaping about every 2s

The cursor timer is firing all the time that you have a fbcon console
registered, whether or not the cursor should be displayed. Someone
looking to save power should probably tackle this such that the cursor
timer doesn't needlessly fire.

But I guess the cellphone people would be more interested in this
problem than the big iron desktop-breaking in-need-of-three-phase-supply
boxen. 8)

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core