Messages in this thread |  | | | Date | Mon, 15 Jun 2009 12:11:20 -0700 | | From | "H. Peter Anvin" <> | | Subject | Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods |
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Peter Zijlstra wrote: > 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 ;-) >
Writing control registers is serializing, so it's a lot more expensive than writing a normal register; my *guess* is that it will be on the order of 100-200 cycles.
That is not based on any actual information.
-hpa
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