System bus saturation?

System bus saturation?

Hello,

I have a 4 Xeon cpu machine(3.0Ghz, IA32 family 15, model2, stepping 6) running Linux. In a performance test, this machine showed poor scalability vs. 4 cpu Itanium machine.

I want to monitor system bus utilization to see if it's already saturated, since this machine FSB is 3.2GB/s, while the IPF machine is 6.4GB/s.

How can I achieve that with vtune(or other tools if applicable)? Seems I can use event based sampling. I found the Xeon CPU tends to be 'Pentium 4 with SSE3' in vtune 7.2 trial, thus what are the system bus events might show value to me? I catched 'Bus accesses from the processor', if it equals to 'n', since this x86 bus data width is 64bit(8 Byte), the bus transfer rate = n / (samping seconds) * 8 [Byte/s] right? Thus it get only ~100 MB/s.

By the way, 'Clockticks' event means All 4 cpus summarized clocks that CPU not in Halt state right? Name it for 'm', Does it mean I can calculate Busy CPU Hz with the equation:

CPU_BUSY_CYCLEs = m / (samping seconds)

Where can I get more informations about the indications of events I get from Vtune? That means, what and how I can get calculate with these events.

Thx a lot.

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