Re: [PATCH] PPC64 collect and export low-level cpu usage statistics

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2005-02-09 at 15:06 -0800, Andrew Morton wrote:
> Paul Mackerras <paulus@samba.org> wrote:
> >
> > POWER5 machines have a per-hardware-thread register which counts at a
> > rate which is proportional to the percentage of cycles on which the
> > cpu dispatches an instruction for this thread (if the thread gets all
> > the dispatch cycles it counts at the same rate as the timebase
> > register).  This register is also context-switched by the hypervisor.
> > Thus it gives a fine-grained measure of the actual cpu usage by the
> > thread over time.
> > 
> > This patch adds code to read this register every timer interrupt and
> > on every context switch.
> 
> fyi: This patch consumes another entry from thread_struct.pad[]. 
> ppc64-implement-a-vdso-and-use-it-for-signal-trampoline.patch consumes two
> more entries, so with both patches, you have none left.

Why couldn't we extend the structure ? That would at worse break modules
binary compatibility, who cares ? :)

Those pads are just stuff that aren't used any more, and back then, when
removing them, we did care about modules binary compat...

Anyways, I don't think there's anything to worry about at this point.
Paul ?

Ben.