Re: [Gems-users] some queries about MOSI_SMP_bcast

[Mike Marty <mikem@xxxxxxxxxxx>]

I'm confused.  The protocol should only deallocate the TBE (MSHR) when it
receives data and does the callback to the processor.  Where do you see it
deallocating as soon as the write is issued to memory?

--Mike


> Hi
>
> I have been playing around with the
> MOESI_SMP_directory protocol and adding the NACK/Retry
> concept in.
>
> I noticed that the protocol deallocates the TBE as
> soon as a write is issued to memory. I was wondering
> if postponing this deallocation to after it goes
> through the memory system , and adding the concept of
> dram nacks for the write request would create some
> sort of incorrect state.
>
> Thanks
> Brinda
>
> --- Mike Marty <mikem@xxxxxxxxxxx> wrote:
>
> > Brinda,
> >
> > > I'm basically integrating our dram simulator
> > framework
> > > into gems. I integrated our simulator into the
> > > MOSI_SMP_bcast cache coherence protocol. It all
> > works
> > > except when the dram system cannot handle a
> > request
> > > and asks the cache hierarchy to retry it later. I
> > > currently have a bad hack to handle this but was
> > > looking to see if any of the SMP protocols handle
> > > retrys.
> > >
> >
> > MOESI_SMP_token might work with no modifications.
> > The Memory controller
> > can simply ignore a request and the token coherence
> > protocol would just
> > time-out and try again.  However if you do use this
> > protocol, set the
> > g_RETRY_THRESHOLD to something higher than 1 (like
> > maybe 10).  After some
> > number of retries specified by this parameter, the
> > token coherence
> > protocol will revert to a heavy-weight request
> > guaranteed to succeed...I
> > suppose this heavy-weight request might not work in
> > your DRAM scheme as
> > your DRAM controller would have to respond to this
> > invoked requeset when
> > it is able to (but doesn't have to right away).
> >
> > Otherwise without thinking about this much, I would
> > think that a
> > directory-based protocol might be more
> > straightforward to implement a
> > nack/retry.
> >
> > > You had mentioned in your email that you had built
> > SMP
> > > protocols in the past which handled acks etc.
> > Would it
> > > be possible for you to send me a version of these
> > > protocols? It would definitely help me in my
> > > integration process.
> > >
> >
> > With have dozens of old protocols in our "attic".
> > The problem is that the
> > Ruby interfaces have changed requiring each protocol
> > be modified to work
> > with the latest release of GEMS.  For example we
> > have a protocol based on
> > the SGI Origin MESI protocol which does
> > Nacks/Retries.  If you wanted, I
> > could probably send this to you but it would _not_
> > work.
> >
> > It would probably just be easiest to take
> > MOESI_SMP_directory, add a NACK
> > response instead of the normal DATA response.  Then
> > in the cache
> > controller upon receiving the NACK, either issue the
> > retry right away or
> > schedule a timeout to wake up some X cycles later to
> > issue the retry.  If
> > you want some more pointers on doing this, let me
> > know.  Start by adding
> > the NACK to CoherenceResponseType in
> > MOESI_SMP_directory-msg.sm.  Create
> > an action in MOESI_SMP_directory-dir.sm to send a
> > NACK.  And so on...
> >
> >
> > --Mike
> >
> >
> >
> > > Thanks
> > > Brinda
> > >
> > > --- Mike Marty <mikem@xxxxxxxxxxx> wrote:
> > >
> > > > > I was trying to better understand the workings
> > of
> > > > the
> > > > > MOSI_SMP_bcast protocol and have a couple of
> > > > > questions.
> > > > >
> > > > > What exactly happens when a request is
> > recycled on
> > > > the
> > > > > network queue i.e. action
> > zz_recycleMandatoryQueue
> > > > in
> > > > > MOSI_SMP_bcast.sm.
> > > > >
> > > >
> > > > Recycling a request pops it from the head of the
> > > > queue and places it at
> > > > the end of the queue, and schedules a wakeup in
> > case
> > > > the controller
> > > > doesn't wake up the next cycle anyways.
> > Essentially
> > > > recycling a request
> > > > allows our queues to be non-FIFO and allows one
> > > > request for cache line to
> > > > block while others are serviced.
> > > >
> > > >
> > > > > What parameter can be used to limit the number
> > of
> > > > > outstanding cache requests?
> > > > >
> > > >
> > > > The number of requests issued to the memory
> > system
> > > > can be controlled by
> > > > the g_SEQUENCER_OUTSTANDING_REQUESTS parameter.
> > > > However the L1 cache
> > > > controller itself can control how many MSHRs are
> > > > available with the
> > > > NUMBER_OF_TBES parameter.
> > > >
> > > >
> > > > > What is the equivalent of the mshr in ruby?
> > > > >
> > > >
> > > > a TBE.  Each protocol will have a TBETable in
> > the
> > > > cache controller.
> > > >
> > > > > Finally unrelated to the MOSI_SMP_bcast
> > protocol -
> > > > are
> > > > > there any SMP protocols which are part of your
> > > > release
> > > > > which can handle retry requests?
> > > > >
> > > >
> > > > We've certainly implemented Nack/Retry directory
> > > > protocols before.  But it
> > > > doesn't appear that the SMP protocols we include
> > > > with the release do this.
> > > >
> > > > The token coherence protocols retry requests.
> > > >
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> > >
> > >
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