Query regarding the sniper-McPat integration

[rahul shrivastava]

Hi,

I am trying to simulate a 3 core system, each core being on separate socket. I am running my multithreaded(3 threads) sample application where each thread just computes a "for loop" for some fixed number of iterations. Each core is running at 2660 MHz. In one of the threads lets say thread A, before starting the "for loop", I decrease the frequency of the core in which thread A is scheduled to 1700 MHz.

After this, I run the simulation and check the xml file which is fed to McPat. In the generated xml file, the frequency of the core in which thread A was scheduled is still set to default 2660 MHz. This seems a bit confusing to me. Could you please shed some light on my following questions

1) If I dynamically change the frequency of the cores from program, multiple times, how would Sniper sim communicate this change of frequency to McPat.

2) Above all, is it even necessary for McPat to know the frequency change that is happening in the simulation?

Regards

Rahul 

[rahul shrivastava]

Hi,

Looking at the script mcpat.py, it seems that mcpat XML is generated by just using sim.cfg and sim.out, but as I said earlier that sim.out has no mention of the number of times the frequency is changed. So, does Sniper Sim has some conservative assumptions about the DVFS functionality?

Regards

Rahul

[Wim Heirman]

Rahul,

mcpat.py does not know about frequency changes, it always uses the initial frequency. So you should not use this script when also using DVFS. The alternative energystats.py script regularly runs McPAT during the simulation, and does use the current frequency at each point in time. So you should use that instead.

Regards,

Wim

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