Re: [Gems-users] Barrnes CPI question

["KS Chow" <g0706256@xxxxxxxxxx>]

I looked at ruby_cycles:

1P: 36,420,634

2P: 64,956,443

 

Shouldn’t it be going down? Or is there something wrong with my simulation?

 

Thanks/Regards.

 

Chow Kian Sim

National University of Singapore

 

From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-bounces@xxxxxxxxxxx] On Behalf Of Dan Gibson
Sent: Wednesday, 16 April, 2008 10:56 PM
To: Gems Users
Subject: Re: [Gems-users] Barrnes CPI question

 

KS Chow wrote:

I have a question regarding the CPI I got from a ruby dump file.

I am comparing the CPI between 2 simulations: a single core machine and a dual-core – all the necessary configurations done in Simics and Ruby (not using Opal).

For the 1-core I ran Barnes with the param indicating 1 processor; the dual-core is run with the param indicating 2 processors.

 

1-core CPI = 3.27789

2-core CPI = 0.621735

The CPI difference could be due to spinning... see below.

 

Is it normal to have such a huge drop in CPI going from 1 to 2 cores? Both have 16Mbs L2 cache and equal amount of L1.

I also noticed that in the 1-core 10,974,780 instructions were executed vs 194,051,043 in the 2-core – why such a big difference in num instructions executed?

Is this caused by the num processors param in Barnes?

SPLASH-2 synchronization is hot-spin intensive. Both CPUs are probably spending a lot of time spinning waiting for the other to set a flag or hit a barrier. Generally we prefer wall clock time (i.e. RUBY_CYCLES) rather than CPI as a performance metric for multiprocessor runs.

 

Thanks/Regards.

 

Chow Kian Sim

National University of Singapore

Regards,
Dan

 

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