Wrong CPU speed reported in mprime benchmark

[James Heinrich]

Another user sent me these benchmarks:

running mprime under openSUSE 11.1 , kernel 2.6.27.9

AMD Athlon(tm) 64 X2 Dual Core Processor 6000+
CPU speed: 1000.55 MHz, 2 cores
CPU features: RDTSC, CMOV, Prefetch, 3DNow!, MMX, SSE, SSE2
L1 cache size: 64 KB
L2 cache size: 1 MB
L1 cache line size: 64 bytes
L2 cache line size: 64 bytes
L1 TLBS: 32
L2 TLBS: 512
Prime95 64-bit version 25.9, RdtscTiming=1
Best time for 768K FFT length: 26.451 ms.
...

Note that the AMD X2 6000+ runs at 3.0GHz (and I confirmed with the user that this was the case -- Prime95 under WINE on the same machine shows 2997.64MHz). Benchmark data is also consistent with running at 3.0GHz.

I'm mostly concerned that if "faulty" benchmark data is being sent back to the server then the collection of benchmark data will get "polluted". In this case the CPU speed is off by 300% so it's fairly easy to see whether it makes sense or not, but a less drastic difference could easily slip by.

[ET_]

Originally Posted by James Heinrich

Another user sent me these benchmarks:Note that the AMD X2 6000+ runs at 3.0GHz (and I confirmed with the user that this was the case -- Prime95 under WINE on the same machine shows 2997.64MHz). Benchmark data is also consistent with running at 3.0GHz.

I'm mostly concerned that if "faulty" benchmark data is being sent back to the server then the collection of benchmark data will get "polluted". In this case the CPU speed is off by 300% so it's fairly easy to see whether it makes sense or not, but a less drastic difference could easily slip by.

Apart from the processor speed detection, are the benchmarks correct?

Luigi

[James Heinrich]

As far as I can tell, benchmarks are completely accurate (assuming the CPU is running at 3.0GHz)

[geoff]

Is frequency scaling active on this machine? One scenario that could cause an incorrect CPU speed report is where the machine is idle and running in at low frequency, then prime95 starts and records that low frequency, then the OS notices that programs are running and ramps up to high frequency, then the benchmark is run.

[James Heinrich]

The user (who I guess reads the forum but doesn't want to post here) said:

Geoff was right: I disabled the "quiet and cool" option in the BIOS setting and now mprime shows 2997.54 Hz.

[willmore]

I have this same issue. When starting Prime95 on a machine for the first time, I have to load the CPU to force C&Q to run the CPU at full speed. It appears that prime95 queries /proc/cpuinfo before doing much work. All that it would need to do to fix this would be to read that information after loading the CPU for a second or two.