a question about Write Combined Transactions on Core 2 Duo

a question about Write Combined Transactions on Core 2 Duo

Hi,

I have a question. I want to measure a number of Write Combined Transactions on my Core 2 Duo using VTune but I don't know what the name of this event.

I found in the VTune help that event BUS_TRANS_BURST counts the sum of all burst transactions such as: burst read, RFO, explicit writeback and Write Combined Transactions.

I.e. BUS_TRANS_BURST = Burst reads + RFOs + explicit writebacks + Write Combine Transactions.

I know that Burst reads in this formula are counted by BUS_TRANS_BRD, RFO are counted by BUS_TRANS_RFO, explicit writebacks are counted by BUS_TRANS_WB. But what event counts Write Combined Transactions?

I understand that Write Combine Transactions can be calculated as following: Write Combine Transactions = BUS_TRANS_BURST - (Burst reads + RFOs + explicit writebacks). But is there a particular event for Write Combined?

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If you got this from the VTune help, no doubt you noticed

Thread Specificity: AT-E FSB_CR_ESCR0

The number of write combining (WC) memory transactions on the bus that originated from the processor core.

In my copy of the help files, it says

BUS_TRANS_BURST

Event Code: 0x6E

Mask: See in table below.

Category: Bus Events;All Events;

Definition: This event counts burst bus transactions

Event Name Extension

Mask

Description

SELF

0x40

This event counts burst (full cache line) transactions including: - Burst reads - RFOs - Explicit writebacks - Write combine lines

ALL_AGENTS

0xE0

This event counts burst (full cache line) transactions including: - Burst reads - RFOs - Explicit writebacks - Write combine lines

so it seems that the transmission of a write combine buffer counts as one such event.

I'm not aware of events which can be used to get a clear indication of write combine buffer thrashing, to mention one possible requirement.

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