Re: No 100 HZ timer !

Andi Kleen
2001-04-10T12:02:18Z

On Tue, Apr 10, 2001 at 12:18:03PM +0100, Alan Cox wrote:
> > > interrupting decrementer. (i.e just about any modern chip)
> >
> > Just how would you do kernel/user CPU time accounting then ? It's currently done
> > on every timer tick, and doing it less often would make it useless.
>
> On the contrary doing it less often but at the right time massively improves
> its accuracy. You do it on reschedule. An rdtsc instruction is cheap and all
> of a sudden you have nearly cycle accurate accounting

Does not sound very attractive all at all on non virtual machines (I see the point on
UML/VM):
making system entry/context switch/interrupts slower, making add_timer slower, just to
process a few less timer interrupts. That's like robbing the fast paths for a slow path.

-Andi