Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

Peter Zijlstra
2009-06-15T19:03:15Z

On Mon, 2009-06-15 at 14:59 -0400, Mathieu Desnoyers wrote:
> * Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:
> > On Mon, 2009-06-15 at 14:48 -0400, Mathieu Desnoyers wrote:
> > > we should not care that much about the performance hit of
> > > saving/restoring the cr2 register at each nmi entry/exit.
> >
> > But we do, perf counters very much cares about nmi performance.
> >
>
> To a point where it cannot afford a simple register save/restore ?
>
> There is "caring" and "_caring_". I am tempted to ask what NMI handler
> execution frequency you have in mind here to figure out if we are not
> trying to optimize sub-nanoseconds per minutes. ;)

Ah, well, I have no idea who expensive cr2 is, if its like a regular
register then it should be fine. If however its tons more expensive then
we should really avoid it.

As to the freq, 100kHz would be nice ;-)