Multi-core Events

Multi-core Events

I am using VTune to measure some multi-core events, including L2 and External Bus events, and get confused about some events' definition.

For L2 Cache Events, they are categorized by BOTH_CORES and SELF, and BOTH_CORES events counts events initiated by either core. Then how to understand the both core here? Then for 8 core processor, Xeon 5355, will this event count part of or all of the actual events happened when 1, 4, and 8 cores were enabled on the machine?

For External Bus Events, there are three categories of events: ALL_AGENTS, SELF and BOTH_CORES.THIS_AGENT. According to the definition, ALL_AGENTS event counts activity initiated by any agent on the bus. In systems where
each processor is attached to a different bus, the count reflects only
the activity for the bus on which the processor resides. Then for 8 core processor, like Xeon 5355, will this ALL_AGENTS event actually count in all events induced by each core when I configure the system to only enable random 4 cores? Or it will only count part of those total actual events due to the internal bus connection architecure?

The VTune I am running is version 8.0.3, OS platform: Fedora Core 6-64bit.

Thanks,
Grace

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