Re: [Gems-users] Question about execution slowdown due to Ruby

["Mike Marty" <mikem@xxxxxxxxxxx>]

Still, I think Mark's Ruby slowdown seems at least an order of magnitude too
much.  Can you try a different target besides cashew?

--Mike


> -----Original Message-----
> From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-
> bounces@xxxxxxxxxxx] On Behalf Of Dan Gibson
> Sent: Friday, December 01, 2006 4:48 PM
> To: Gems Users
> Subject: Re: [Gems-users] Question about execution slowdown due to Ruby
> 
> Mark,
> 
> We've actually looked extensively at this.
> 
> Background: the 10x number is for a much earlier version of Simics
> (pre-2.0 if I am not mistaken) and an earlier version of Ruby, with
> cpu-switch-time 1000. 10x is about right for the timing of the
> Tourmaline functional simulator... Ruby is now much slower relative to
> Simics... because:
> 
> Firstly, Simics 3+ runs in "fast" mode by default, whereas Simics 2.X
> and earlier ran in "stall" mode by default. For that and due to other
> optimizations, Simics 3+ is significantly faster than Simics 2.X in
> standalone mode (eg without timing modules).
> 
> Second, I'm not entirely familiar with the cashew target... (not
> familiar at all, in fact). There might be something to do with that
> particular target that creates slowdown.
> 
> Third, the majority of the added slowdown actually occurs *within
> Simics*, not within Ruby. We discovered this when when profiling Ruby's
> execution time. Our theory is that Simics behaves differently when alien
> modules (eg Ruby) are installed. Moreover, Simics does not easily
> optimize stall times of large sizes. You can test this theory yourself
> by building a trivial timing module and examining its behavior. The best
> performance we ever attained with a trivial timing module was around 10x
> for Simics 2.0.x, around 30x for Simics 2.2.x, and around 100x for
> Simics 3.0, both with 0-cycle memory accesses.
> 
> There are a few things you can do to improve your simulator performance:
> 1) Limit Simics' memory to just below the available space of your host.
> set-memory-limit is the appropriate simics command
> 2) Set cpu-switch-time to something large... this sacrifices some
> fidelity.
> 3) Use smaller latencies -- host execution time is roughly proportional
> to target execution time.
> 
> 
> Regards,
> Dan Gibson
> 
> Mark Gebhart wrote:
> > Hi,
> >
> > I am running some tests using MOSI_SMP_bcast with a 4 processor target
> > machine using cashew-common.simics.  I have set the memory size in both
> Ruby
> > and the simics config file to 4 GB.
> >
> > I wrote a short vector add test program and compared the time to
> simulate on
> > simics with and without Ruby loaded.  Ruby+simics is between 2000 and
> 3000
> > times slower than just simics.  I changed all of the cache latencies to
> be 1
> > cycle and then Ruby+simcs was between 200 and 300 times slower than just
> > simcs.  Are these slowdowns in line with what others have observed?  I
> saw
> > in an archived message on this list that perhaps a slowdown closer to
> 10x
> > would be expected.
> >
> > I am using simics 3.0-22 and GEMS 1.3, my host machine is a 2.8 GHZ P4
> with
> > 1G of RAM and nothing else running during simulation.   The simics
> process
> > stays at 100% utilization throughout the execution.
> >
> > I have compiled Ruby with the following optimization flags:
> > -O2 -finline-functions -DNO_VECTOR_BOUNDS_CHECKS -
> DMULTIFACET_NO_OPT_WARN
> >
> > I use the -stall flag to simics and then issue the following commands:
> >
> > read-configuration ../../checkpoints-u3/linux-a.out-sun-4p.check
> > instruction-fetch-mode instruction-fetch-trace
> > istc-disable
> > dstc-disable
> > cpu-switch-time 1
> > load-module ruby
> > ruby0.setparam g_NUM_PROCESSORS 4
> > ruby0.init
> > con0.input "/usr/mark/a.out\n"
> > c
> >
> > Did I perhaps misconfigure something that is causing a large slowdown?
> Any
> > insight or advice would be greatly appreciated.
> >
> > Thanks,
> > Mark
> >
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> 
> --
> http://www.cs.wisc.edu/~gibson [esc]:wq!
> 
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