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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