RE: [Gems-users] Different CPI's for Ruby and Opal

[Bradford Beckmann <beckmann@xxxxxxxxxxx>]

The OPAL_RUBY_MULTIPLIER is simply a frequency multiplier between Ruby's
and Opal's frequencies.  If you set it to 1, Opal and Ruby have the same
frequency, higher Opal will have a faster frequency.

The multiplier was added as a performance enhancement.  The assumption is
Opal needs a high frequency to model a fast out-of-order processor, but
Ruby can use a lower frequency because it models the relatively slow
memory system.  Since Ruby is an eventqueue driven simulator, having a
slower frequency in Ruby results in less 'wakeup' cycles and thus reduces
simulation time.

However, when using a non-unit multiplier, you need to remember the
relation when analyzing the stats.


On Thu, 28 Apr 2005, Jonathan Brooks wrote:

> Yes, they are off exactly by a factor of two!  Ok, but what is the
> purpose OPAL_RUBY_MULTIPLIER?  Can I set it to 1 without affecting
> something else?
>
> -----Original Message-----
> From: gems-users-bounces@xxxxxxxxxxx
> [mailto:gems-users-bounces@xxxxxxxxxxx] On Behalf Of Mike Marty
> Sent: Thursday, April 28, 2005 6:39 PM
> To: Gems Users
> Subject: Re: [Gems-users] Different CPI's for Ruby and Opal
>
> Are they off by a factor of 2?  If so, this is due to the
> OPAL_RUBY_MULTIPLIER setting in ruby/config/rubyconfig.defaults
>
> --Mike
>
>
> > I am running a CMP system (2 procs on 1 chip) with Serengeti/Solaris
> > target (mostly default configuration).  I use both Opal and Ruby for a
> > simulation of running a few binaries for 1 million steps.  When I look
> > at the statistics in Ruby, I see Instructions per cycle per processor,
> > which I assume I can take the inverse to get Cycles Per Instruction).
> > However these numbers do not match the CPI's I get in Opal's report.
> > Why are they different?
> >
> >
> >
> >
> >
> >
> >
> >
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