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

[Ingo Molnar]

* Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> wrote:

> * Peter Zijlstra (a.p.zijlstra@xxxxxxxxx) 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. ;)

I routinely run 'perf' with half a million NMIs per second or more. 
( Why wait 10 seconds for a profile you can get in 1 second? ;-)

Granted that is over multiple CPUs - but still performance does 
matter here too.

Reading cr2 is certainly fast. Writing it - dunno.

	Ingo
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