llvm dev - Nov 2015 - Is there a way to convert between SchedMachineModel and Itineraries?

----- Original Message -----
> From: "Rail Shafigulin via llvm-dev" <llvm-dev at
lists.llvm.org>
> To: "llvm-dev" <llvm-dev at lists.llvm.org>
> Sent: Monday, November 9, 2015 10:09:07 AM
> Subject: Re: [llvm-dev] Is there a way to convert between SchedMachineModel
and Itineraries?
> 
> 
> Anybody? Does anyone at all know how to do it?
There is no direct conversion. Although they are similar models, they are
different. The strength of Itineraries lies in modeling pipelines with complex
hazards (especially those that are not fully pipelined, or have other similar
ordering constraints). SchedMachineModel can't do that. Unless you need to
represent those kinds of constraints, SchedMachineModel is preferred. We'd
like to move toward using SchedMachineModel for most things.

 -Hal
> 
> On Friday, November 6, 2015, Rail Shafigulin < rail at esenciatech.com
>
> wrote:
> 
> 
> 
> Is there a way to convert between SchedMachineModel and Itineraries?
> 
> 
> I was trying to write a very simple VLIW packetizer (Hexagon was my
> starting point). It turns out that current DFAPacketizer is using
> itineraries, but my schedule is based on SchedMachineModel (I was
> recommended to use it since the itineraries are being phased out). I
> was wondering if there is an automated tool that would convert from
> SchedMcahineModel to Itinerary based mode? As far as I understand
> they both convey the same information so there should be a way to
> convert between them.
> 
> --
> 
> 
> 
> 
> Rail Shafigulin
> Software Engineer
> Esencia Technologies
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory

On Mon, Nov 9, 2015 at 10:31 AM, Hal Finkel <hfinkel at anl.gov> wrote:
> ----- Original Message -----
> > From: "Rail Shafigulin via llvm-dev" <llvm-dev at
lists.llvm.org>
> > To: "llvm-dev" <llvm-dev at lists.llvm.org>
> > Sent: Monday, November 9, 2015 10:09:07 AM
> > Subject: Re: [llvm-dev] Is there a way to convert between
> SchedMachineModel   and Itineraries?
> >
> >
> > Anybody? Does anyone at all know how to do it?
>
> There is no direct conversion. Although they are similar models, they are
> different. The strength of Itineraries lies in modeling pipelines with
> complex hazards (especially those that are not fully pipelined, or have
> other similar ordering constraints). SchedMachineModel can't do that.
> Unless you need to represent those kinds of constraints, SchedMachineModel
> is preferred. We'd like to move toward using SchedMachineModel for most
> things.
>
>  -Hal
>
Thanks for the reply Hal. I thought my thread was dead.

I was recommended to use SchedMachineModel for my VLIW, which is what I've
done (it took me a month to learn tblgen and write the scheduling model and
one more month do get my head around LLVM. My experience with compilers is
limited to a class I took in college a year ago). The scheduling part seems
to be working (at least this is what my limited testing shows). However
current DFAPacketizer is based on itineraries (DFAPacketizer.cpp, lines
66-73). I was hoping there is a way to convert between these two
representations so that I wouldn't have to rewrite the packetizer.
Unfortunately my experience with compilers is very limited and I still have
a lot to learn.

Right now I have two options. In both of the cases there are significant
drawbacks.
1. Rewrite the scheduling model using itineraries. Unfortunately there is
very little help available on this topic, I even asked on the IRC channel
and nobody seems to know how it is done, since everyone is moving towards
the SchedMachineModel.
2. Write a new packetizer which will use the SchedMachineModel, however, as
I said before, I have a very limited experience with compilers and this
looks like some major work. I'm not afraid of it, it is just there is not
much information and help available.

I would greatly appreciate any help on this

Rail
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> On Nov 9, 2015, at 10:49 AM, Rail Shafigulin <rail at
esenciatech.com> wrote:
> 
> On Mon, Nov 9, 2015 at 10:31 AM, Hal Finkel <hfinkel at anl.gov
<mailto:hfinkel at anl.gov>> wrote:
> ----- Original Message -----
> > From: "Rail Shafigulin via llvm-dev" <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
> > To: "llvm-dev" <llvm-dev at lists.llvm.org
<mailto:llvm-dev at lists.llvm.org>>
> > Sent: Monday, November 9, 2015 10:09:07 AM
> > Subject: Re: [llvm-dev] Is there a way to convert between
SchedMachineModel   and Itineraries?
> >
> >
> > Anybody? Does anyone at all know how to do it?
> 
> There is no direct conversion. Although they are similar models, they are
different. The strength of Itineraries lies in modeling pipelines with complex
hazards (especially those that are not fully pipelined, or have other similar
ordering constraints). SchedMachineModel can't do that. Unless you need to
represent those kinds of constraints, SchedMachineModel is preferred. We'd
like to move toward using SchedMachineModel for most things.
> 
>  -Hal
> 
> Thanks for the reply Hal. I thought my thread was dead. 
> 
> I was recommended to use SchedMachineModel for my VLIW, which is what
I've done (it took me a month to learn tblgen and write the scheduling model
and one more month do get my head around LLVM. My experience with compilers is
limited to a class I took in college a year ago). The scheduling part seems to
be working (at least this is what my limited testing shows). However current
DFAPacketizer is based on itineraries (DFAPacketizer.cpp, lines 66-73). I was
hoping there is a way to convert between these two representations so that I
wouldn't have to rewrite the packetizer. Unfortunately my experience with
compilers is very limited and I still have a lot to learn.
> 
> Right now I have two options. In both of the cases there are significant
drawbacks.
> 1. Rewrite the scheduling model using itineraries. Unfortunately there is
very little help available on this topic, I even asked on the IRC channel and
nobody seems to know how it is done, since everyone is moving towards the
SchedMachineModel.
Not many people work with either the machine model or itineraries.

Be careful! I think the DFAPacketizer will only be effective on a very simple
itinerary (which could easily have been expressed in the new machine model
instead). I’ve heard stories of it “blowing up” on large itineraries. I have no
direct experience with it.
> 2. Write a new packetizer which will use the SchedMachineModel, however, as
I said before, I have a very limited experience with compilers and this looks
like some major work. I'm not afraid of it, it is just there is not much
information and help available.
This looks like an opportunity for you to learn something interesting.
Generating a state machine from a set of constraints is fairly straightforward.
The only difficultly lies in limiting the total number of states so you don’t
end up with a giant table. If you were able to express those constraints in the
machine model they must not be too complicated.

If your state machine is really just modeling the number of functional units
that can be used by a given VLIW bundle, then you don’t need to generate a state
machine at all. All you need are counters. MachineScheduler can do this for you.
It already has some support for scheduling instruction groups for a simple
in-order machine (without plugging in your own scheduler at all). Currently,
this isn’t fully implemented—it isn’t modeling multiple functional units per
cycle. But that would be *very* easy to fix and is something I could help with.
It’s just that no one has asked for it.

Andy
> 
> I would greatly appreciate any help on this
> 
> Rail
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