Rob Hudson wrote:
> The Linux kernel v2.6.21 is out and Linus says:
>
> So the big change during 2.6.21 is all the timer changes to support a
> tickless system (and even with ticks, more varied time sources).
> Source: http://lkml.org/lkml/2007/4/25/561
>
> What's it mean to be "tickless"?
Since time immemorial, the Unix kernel has programmed the system clock
to interrupt at fixed intervals. On the PDP-11, the interrupt was
every 1/60th of a second. On the VAX running BSD, it was every
1/100th of a second. Linux kernel 2.6.20 uses a default interval of
1/1000th of a second, but it's a config option.
Obviously, there's a lot of overhead in processing all those
interrupts. If you're running a number of virtual machines, and all
the virtual machines are handling an interrupt every millisecond,
that's even more overhead.
A tickless system does away with the fixed interval. Instead, it
looks at the timer queue and programs the clock to interrupt when the
first timer is about to expire. Whenever a timer is added to or
removed from the queue, the clock might have to be reprogrammed.
The advantages are:
* "normal" systems - less interrupt processing overhead
* idle VMs - minimal to no CPU overhead
* mobile CPUs - can use a reduced power state for longer battery life
--
Bob Miller K<bob>
[EMAIL PROTECTED]
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