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

Andi Kleen
2005-11-30T00:34:36Z

On Wed, Nov 30, 2005 at 10:56:26AM +1100, David Gibson wrote:
> On Wed, Nov 30, 2005 at 12:39:20AM +0100, Andi Kleen wrote:
> > > Well, if that's all you want them to use RDPMC 0 for, why not just make
> > > PMCs programmable from userspace?
> >
> > First we need to have a cycle counter PMC anyways for the NMI watchdog.
> > So it can as well be used for other purposes.
>
> But the watchdog doesn't require it to be in the same place on all
> machines. Exporting it turns an internal requirement into an ABI
> point.

Yes, but the only alternative I know of would be to let user space
continue getting broken all the time with RDTSC. RDPMC is a nice
alternative.

-Andi