Hello, We've gotten helpful replies on related problems a few months ago, so I hope someone here is able to help us out with this mystery too.
We are comparing micro-operation counts between three generations of Intel processors, and are unable to make sense of them. I've attached a barplot graph to this mail, showing micro-ops per instruction rates for SPEC CPU2006 on the three different processor generations.
<<inline: mops_per_inst_speccpu2006.jpg>>
The counts were obtained using the perfex tool that comes with the perfctr kernel patch, and using the following events: *) Intel Pentium 4: uops_retired (perfex -e ) *) Intel Core 2: UOPS_RETIRED.ANY (perfex -e 0x410FC2) *) Intel Core i7: UOPS_RETIRED.ANY (perfex -e 0x4101C2) The thing we are unable to explain is that the micro-ops per instruction rate rises significantly when comparing Core i7 (Nehalem architecture)to Core 2 (Core architecture). And that while micro-op fusion is reported
to be improved in the more recent Core i7 processors. Same goes for the significant drop when comparing Pentium 4 to Core 2:the uops/instr. rate drops from 1.41 on average on Pentium 4 to just 1.08
on Core 2 (Core i7: 1.32 on average). This suggests that something might be wrong with some of the micro-ops counts were are getting through these specific events, most probably with the Core 2 counts being too low.I'd like to stress that the instruction counts are not to blame here; these match within a 1% range across the three different processor generations.
Of course we'r using the exact same binaries on all three systems. Has anyone noticed similar issues when comparing micro-op counts across processor familes? Is anyone aware of bugs in the performance counters that might explain these numbers? Is there any way we can get some feedback from Intel, to make sure we are doing everything correctly, and maybe that's were stumbling into a known processor bug or some such? greetings, Kenneth
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