Inaccuracy from Memory read/write bytes when using PCM-2.11 on Core i7 5960X Haswell-E

[ZWang45]

Hi All,

I try to use PCM-2.11 to measure the memory read/write bytes on Intel I7 5960X Processor Extreme Edition. 

The example “for (int i = 0; i < 200000000; i++) (int *)p_data = i;” is compiled with ICC 16.0.3.   

I have checked the assemble of the store instruction: movdqa. It means each cache line will be read first.

The PCM result shows:

BytesReadFromMC: 47615872 (wrong number)

BytesWrittenToMC: 808465920 (right number).

Do I need to modify the lines in cpucounters.cpp:  

void ServerPCICFGUncore::program()
{
    uint32 MCCntConfig[4] = {
        MC_CH_PCI_PMON_CTL_EVENT(0x04) + MC_CH_PCI_PMON_CTL_UMASK(3),  
        MC_CH_PCI_PMON_CTL_EVENT(0x04) + MC_CH_PCI_PMON_CTL_UMASK(12),    
    };

Thanks. 

[McCalpinJohn]

It looks like this is an attempt to measure behavior for the initial access to the array.   The behavior of the system for page instantiation may not be what you expect. 

I recommend that you add more loops to read/write the data after it is initialized, and that you make the number of times the data is accessed after initialization an easy-to-modify variable.  You should then see that you get the expected memory access counts for subsequent accesses.