a question about Write Combined Transactions on Core 2 Duo

a question about Write Combined Transactions on Core 2 Duo

nserdjuk's picture

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?

2 posts / 0 new
Last post
For more complete information about compiler optimizations, see our Optimization Notice.
TimP (Intel)'s picture

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.

Login to leave a comment.