Re: How to measure time accurately.

[Chris Friesen]

Peter Chubb wrote:
> > > > > > "Chris" == Chris Friesen <cfriesen@xxxxxxxxxx> writes:

> Chris> Most cpus have some way of getting at a counter or decrementer
> Chris> of various frequencies.  Usually it requires low-level hardware
> Chris> knowledge and often it needs assembly code.
>
> As a device driver is inside the linux kernel (unless you're writein a
> user-mode device driver :-)) you can use the getcycles() macro that's
> defined for most architectures.  It provides a snapshot of the
> cycle-counter.

For ppc this only gives 32-bit values, which overflow every 129 seconds 
on my G5.  Depending on how long you're trying to time, this could be a 
problem.

Chris
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/