Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt.

Andi Kleen
2005-05-17T13:58:39Z

> > + help
> > + 100 HZ is a typical choice for servers, SMP and NUMA systems
> > + with lots of processors that may show reduced performance if
> > + too many timer interrupts are occurring.
>
> One of the options should mention the power savings benefit on laptops.
> How about:

Actually it is not 100% clear. The ACPI idle code relies on
the timer right now to go from C1 to C2/C3. It basically
goes down in a staircase, first staying in C1, then when woken
up and still idle go down lower etc.

With HZ=100 the minimal latency (assuming no other interrupts) to go from C1
to C2 is 10ms, not 1ms, which might be even a power loss in some workloads.

-Andi

P.S.: The SUSE 2.4 kernels had for some time variable HZ, settable at boot.
It surprisingly didn't cause too much slowdown or code bloat and only
needed minor fixes over the tree. Might be worth considering at least
as a CONFIG