* H. Peter Anvin (hpa@xxxxxxxxx) wrote: > Peter Zijlstra wrote: > > On Mon, 2009-06-15 at 14:59 -0400, Mathieu Desnoyers 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. ;) > > > > 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. > Then how about just writing to the cr2 register *if* it has changed while the NMI handler was running ? if (unlikely(read_cr2() != saved_cr2))) write_cr2(saved_cr2) Mathieu > -hpa > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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