Re: dynamic-hz

[Russell King <rmk+lkml@arm.linux.org.uk>]

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