Access Contention Analysis

[Divino_C_]

Hello.

I'm using Vtune Amplifier Update 9 on my Ubuntu 12.04.03 machine which is an i7-3630QM (Ivy Bridge). The problem is that in Vtune I see a set of analysis under "Sandy Bridge / Ivy Bridge / Haswell" folder, however Vtune only let me do the "General Exploration" and "Badwidth" analysis. When I choose other analysis (under the same folder), like "Access Contention", it says "This analysis type is not applicable to the current machine microarchitecture.", is this a bug or I'm understanding something wrong here? Isn't my machine Ivy Bridge Ô.o?

Thanks.

[Peter_W_Intel]

First at all, suggest to try latest Update 13. If problem still persists on, check if associated event is supported for current processor.

Access Contention: formula

% of cycles spent accessing data modified by another core:
( MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS * 84) / CPU_CLK_UNHALTED.THREAD

Can you use "amplxe-runss event-list | grep  MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS" to know if Access Contention analysis is supported?

[Divino_C_]

Hi Peter.

I'll give a try in Update 13. Here is the output of -event-list:

MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_MISS
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HIT
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_NONE
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_MISS_PS
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HIT_PS
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS
MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_NONE_PS

Thank you,
César. 

[Divino_C_]

Same problem as before.

[Peter_W_Intel]

If event MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS is supported, you can use cmd -

amplxe-cl -collect-with runsa -knob event-config=CPU_CLK_UNHALTED.THREAD,INST_RETIRED.ANY,MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS -- application

to get performance data. When

( MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_HITM_PS * 84) / CPU_CLK_UNHALTED.THREAD

Thresholds: Investigate if –
% cycles accessing modified data > .05

If don't know why metric of "Access Contention Analysis" is not applicable on GUI? If you can use events in cmd, you also can get result and decide if you need to investigate in code.

You also can try command line -

amplxe-cl -collect snb-access-contention -- ./application

What happens? Do you need to uninstall the tool, remove install dir , then reinstall the tool?

Regards, Peter

[Divino_C_]

Hi Peter, thanks!

I'll give it a try and post here the results.

Follow up question: This "* 84" means that a HITM on LLC cost 84 cycles right? Do you know the values for a clean HIT (cross core) and a L3 hit (without snoop)?

[Peter_W_Intel]

"84" means penalty cycles for LLC HIT with snoop.

MEM_LOAD_UOPS_RETIRED.LLC_HIT_PS is for LLC HIT without snoop, penalty cycles are "36"

[Bernard]

Thanks for providing an explanation. I was also puzzled by those constants.

[Vitaly_S_Intel]

Answer on original question

[qi_z_1]

I have the same problem. I'm using Vtune Amplifier Update 13 on my windows 7. My CPU is intel i3770K. Is there any solution on windows 7?