Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default

Nicholas Miell
2005-11-29T21:43:24Z

On Tue, 2005-11-29 at 19:13 +0100, Andi Kleen wrote:
> > Where did you see that PMC0 (PERSEL0/PERFCTR0) can only be programmed
> > to count cpu cycles (i.e. cpu_clk_unhalted)? As far as I can tell from
> > the documentation, the 4 counters are symetrical and can measure
> > any event that the processor offers.
>
> Linux NMI watchdog does that.
>
> All other perfctr users are supposed to keep their fingers away
> from the watchdog (it looks like oprofile doesn't but not for much
> longer ...)

Why? Hardcoding PMC 0 to be a cycle counter seems to be a waste of a
perfectly usable performance counter. What if I want to profile four
things, none of them requiring a cycle count?

--
Nicholas Miell <nmiell@comcast.net>