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

Andi Kleen
2005-11-29T23:39:22Z

> 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.

And using virtual performance counters adds a large cost the
context switch for changing the MSRs around. An always running counter
avoids this problem.

-Andi