Re: [Gems-users] Barrnes CPI question

[Dan Gibson <degibson@xxxxxxxx>]

Try simulating the parallel section only. I think thats why you're 
seeing unexpected results. It happens a lot on this list. You'll also 
find that simulator time is noticeably reduced, as well.
Regards,
Dan

KS Chow wrote:
> The entire thing - but the results are really unexpected.
>
> Thanks/Regards.
>
> Chow Kian Sim
> National University of Singapore
>
> -----Original Message-----
> From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-bounces@xxxxxxxxxxx]
> On Behalf Of Dan Gibson
> Sent: Wednesday, 16 April, 2008 11:35 PM
> To: Gems Users
> Subject: Re: [Gems-users] Barrnes CPI question
>
> Are you simulating the entire execution or just the parallel section? 
> The entire execution includes thread creation and destruction, which 
> could account for the slowdown.
> Regards,
> Dan
>
> KS Chow wrote:
>   
> > 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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