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

["Mark Gebhart" <mgebhart@xxxxxxxxxxxxx>]

Thanks for the info, I will try the sarek target and see what sort of
slowdowns I see.

Mark

-----Original Message-----
From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-bounces@xxxxxxxxxxx]
On Behalf Of Mike Marty
Sent: Friday, December 01, 2006 5:40 PM
To: 'Gems Users'
Subject: Re: [Gems-users] Question about execution slowdown due to Ruby

Mark,  

A couple years ago we collected these slowdown numbers with Simics 2.0.x
running the Sarek target (I believe):

http://www.cs.wisc.edu/gems/isca_tutorial.ppt#79

--Mike

> -----Original Message-----
> From: gems-users-bounces@xxxxxxxxxxx [mailto:gems-users-
> bounces@xxxxxxxxxxx] On Behalf Of Mark Gebhart
> Sent: Friday, December 01, 2006 5:06 PM
> To: Gems Users
> Subject: Re: [Gems-users] Question about execution slowdown due to Ruby
> 
> Mike,
> 
> Is there a particular target you have experience with so that I could try
> that and compare results to what you have seen?
> 
> Thanks for the help,
> Mark
> 
> On Fri, 1 Dec 2006, Mike Marty wrote:
> 
> > 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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> >
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