Re: [Gems-users] Do you have the plan to support the Dragonprotocol inGEMS?

[郭锐 <timmyguo@xxxxxxxxxxxxxxxx>]

In fact, I was inspired by a TLS system based on the Stanford Hydra CMP.
I think it's more suitable to implement a TLS system base on an updating
protocol. Currently I use a system modified from LogTM to do my experiments.
And I found that it suffers badly from false sharing and the performance
drops dramatically when the data dependences are high. And a updating
protocol fits this situation quite well. So I begin to search for a
simulation platform that supports updating protocol such as dragon.
PS: The Hydra CMP also uses a write-through L1 and a shared L2. I'm
wondering how much bandwidth would it be needed to support such a
configuration.

> -----Original Message-----
> From: gems-users-bounces@xxxxxxxxxxx
[mailto:gems-users-bounces@xxxxxxxxxxx]
> On Behalf Of Milo Martin
> Sent: Monday, June 18, 2007 2:17 PM
> To: Gems Users
> Subject: Re: [Gems-users] Do you have the plan to support the
Dragonprotocol
> inGEMS?
> 
> I agree with Mike's assessment that update protocols are
> challenging.  However, I would strengthen his comment to say that
> update protocols aren't just challenging in GEMS, they are
> challenging to implement in *real* systems as well.  The memory
> consistency model issues become really complicated really quickly.  I
> think this is one of the main reasons that most real systems today
> use invalidation-based cache coherence protocols.  Sure, there are
> some issues with write-through L1s to a shared L2 used in systems
> such as IBM's  Power4, but that isn't as bad as a full update
> protocol.  I just can't think of a example of a high-performance
> multiprocessor with an update protocol built in the last decade (or
> longer).
> 
> For this reason, the Ruby/SLICC part of GEMS explicitly focuses only
> on block-level coherence (which usually implies invalidation-based
> cache coherence).  Modifying GEMS to support update-based coherence
> could be done, but most of SLICC would need to be removed (or heavily
> modified) to do so.
> 
> - Milo
> 
> On Jun 17, 2007, at 7:57 AM, Mike Marty wrote:
> 
> > I think implementing any update protocol is a challenge in GEMS
> > because of
> > memory consistency issues.  The Simics functional simulation
> > implements
> > sequential consistency, and this might be hard with an update protocol
> > (especially without an atomic bus)
> >
> > --Mike
> >
> >
> > ----- Original Message -----
> > From: "??" <timmyguo@xxxxxxxxxxxxxxxx>
> > To: <gems-users@xxxxxxxxxxx>
> > Sent: Sunday, June 17, 2007 4:38 AM
> > Subject: [Gems-users] Do you have the plan to support the Dragon
> > protocol
> > inGEMS?
> >
> >
> >> Dear GEMS TEAM,
> >> I recently find that a dragon protocol simulation would be
> >> beneficial to
> >> my
> >> research. And GEMS doesn't implement this. Do you have a plan on
> >> this?
> >>
> >> As far as I know, the SLICC language & compiler handles memory
> >> transaction
> >> in per-line basis. I think it's crucial for an updating protocol
> >> to handle
> >> transaction in per-word basis, which not only eliminates false
> >> sharing but
> >> also reduces bandwidth consumption. Do you have a plan to
> >> implement this?
> >>
> >> G.R.
> >>
> >> _______________________________________________
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> >
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> >
> 
> --
> Milo M. K. Martin (milom@xxxxxxxxxxxxx)
> http://www.cis.upenn.edu/~milom/
> Assistant Professor
> Computer and Information Sciences Department
> University of Pennsylvania
> 
> 
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