Re: [Gems-users] simulating perfect L2 for CMP

[Dan Gibson <degibson@xxxxxxxx>]

PERFECT_MEMORY_SYSTEM = true implies that *all* memory requests will 
observe the same latency. That latency is PERFECT_MEMORY_SYSTEM_LATENCY. IE
PERFECT_MEMORY_SYSTEM: true
PERFECT_MEMORY_SYSTEM_LATENCY: 0
would imply that ALL requests are completed in zero time.

To set the main memory latency to zero:
MEMORY_RESPONSE_LATENCY_MINUS_2: -2
and change the definition of memoryResponseLatency() in RubyConfig.h to 
simply return MEMORY_RESPONSE_LATENCY_MINUS_2 + 2.
Regards,
Dan

Thomas Yeh wrote:
> Thx for the suggestion. I need the protocol to be simulated, so I'll have 
> to run opal and ruby.
> I assume that setting the memory latency to zero 
> involves setting PERFECT_MEMORY_SYSTEM to true and 
> PERFECT_MEMORY_SYSTEM_LATENCY to 0.
> PERFECT_MEMORY_SYSTEM: false
> PERFECT_MEMORY_SYSTEM_LATENCY: 0
>
>
> On Mon, 9 Oct 2006, Dan Gibson wrote:
>
>   
> > I recommend you set the memory latency to zero.
> >
> > My other comments follow:
> >
> > Thomas Yeh wrote:
> >     
> > > I am currently simulating with the MOESI_CMP_directory protocol, and would
> > > like to run the simulations with a perfect L2.
> > >
> > > What is the best way to do this?
> > > 1) Running opal without ruby and specifing L2_IDEAL?
> > >
> > >       
> > Running without ruby doesn't simulate any cache coherence. Unless this
> > is what you're intending, running without Ruby is probably a bad option.
> >     
> > > 2) Run both opal and ruby, but specify L2 is always a hit locally?
> > >
> > >       
> > Yes, you could do that.
> >     
> > > Is the L1 always 1 cycle when running opal w/o ruby? I don't see
> > > a parameter for setting the L1 latency.
> > >
> > >       
> > Opal w/o Ruby uses its own cache model, based on a uniprocessor
> > hierarchy. See Opal's cache.[Ch].
> >     
> > > If I run without ruby, how do I compare the performance? Since there won't
> > > be a ruby_cycle metric.
> > >
> > >       
> > Opal will still produce several metrics. Pick your favourite and use
> > that instead.
> >     
> > > thx,
> > > Tom
> > >
> > >       
> > Regards,
> > Dan
> >     
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