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March 4, 2008 DF3-3http://csg.csail.mit.edu/arvind/ Dynamic Dataflow Architectures Allocate instruction templates, i.e., a frame, dynamically to support each loop iteration and procedure call termination detection needed to deallocate frames The code can be shared if we separate the code and the operand storage frame pointer instruction pointer a token
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March 4, 2008 http://csg.csail.mit.edu/arvind DF3-1
Dynamic Dataflow
ArvindComputer Science & Artificial Intelligence LabMassachusetts Institute of Technology
March 4, 2008 DF3-2http://csg.csail.mit.edu/arvind/
Static Dataflow:Problems/Limitations
Mismatch between the model and the implementation
The model requires unbounded FIFO token queues per arc but the architecture provides storage for one token per arc
The architecture does not ensure FIFO order in the reuse of an operand slot
The merge operator has a unique firing ruleThe static model does not support
Function calls Data Structures
- No easy solution in the static framework- Dynamic dataflow provided a framework for solutions
March 4, 2008 DF3-3http://csg.csail.mit.edu/arvind/
Dynamic Dataflow Architectures
Allocate instruction templates, i.e., a frame, dynamically to support each loop iteration and procedure call
termination detection needed to deallocate frames
The code can be shared if we separate the code and the operand storage
<fp, ip, port, data>
frame pointer
instruction pointer
a token
March 4, 2008 DF3-4http://csg.csail.mit.edu/arvind/
A Frame in Dynamic DataflowProgram1
2345
+
*-+
3
1
2
4
5
3L, 4L3R, 4R
5L5Rout*
a b
+ *7
- +
*
yx
1 2
3 4
5
Need to provide storage for only one operand/operator
<fp, ip, p , v>
12
45
73
Frame
March 4, 2008 DF3-5http://csg.csail.mit.edu/arvind/
Data Structures in Dataflow
. . . . PP
MemoryData structures reside in a structure store tokens carry pointers
I-structures: Write-once, Read multiple times or allocate, write, read, ..., read,
deallocate No problem if a reader arrives
before the writer at the memory location
I-fetch
a
I-store
a v
March 4, 2008 DF3-6http://csg.csail.mit.edu/arvind/
I-Structure Storage: Split-phase operations & Presence bits
I-Fetch
t
<s, fp, a >s
1234a
aaa
v2fp.ip
I-structureMemory
• Need to deal with multiple deferred reads • other operations: fetch/store, take/put, clear
v1
address to be read
t
I-Fetch <a, Read, (t,fp)>s
split phase
forwarding address
March 4, 2008 DF3-7http://csg.csail.mit.edu/arvind/
Dynamic Dataflow Graphs
March 4, 2008 DF3-8http://csg.csail.mit.edu/arvind/
Firing Rules
Input tokens must have identical tags
+
<c•s,x>L <c•s,y>R
s:
t1:
L R
t2:
+S:
t2:t1:
<c•t1,x+y>p1 <c•t2,x+y>p2
p1 p2
context (fp)inst no (ip)port
March 4, 2008 DF3-9http://csg.csail.mit.edu/arvind/
Well Behaved Graphs• • •
• • • • • •
• • •c • s1 c • sn
c • t1 c • tm
1. One-in-one-out property.2. Self Cleaning: Initially the graph contains no tokens; when all the output tokens have been produced no tokens remain in the graph.
March 4, 2008 DF3-10http://csg.csail.mit.edu/arvind/
Consequences of TaggingNo need of merge in well behaved dataflow graphs.
Even if f(x1) completes after g(x2) the output tokens will carry the "correct" tag.
X
F T
x2x1
T F
f g
March 4, 2008 DF3-11http://csg.csail.mit.edu/arvind/
Making Graphs Well BehavedSometimes extra inputs and outputs have to be provided to make graphs well behaved.
constants
3 3trigger input.
March 4, 2008 DF3-12http://csg.csail.mit.edu/arvind/
Making Conditionals
Well BehavedAll unconnected outputs of switches are collected to generate a signal.
X Yb
p f
T F T F
X
signal
X
S
March 4, 2008 DF3-13http://csg.csail.mit.edu/arvind/
I-Structure Operations
I-store I-store
vs
t p
s
t pI-structure Storage
< , "write", v>
signal
I-store: <c•s, >1 x <c•s,v>2 < ,"write",v> x <c•t,_>p
address value signal
I-store won't be well behaved without a signal output
March 4, 2008 DF3-14http://csg.csail.mit.edu/arvind/
Well Behaved Blocks
All the signals in a block or a procedure are collected via a tree of synchronizing gates to generate a single signal.
signal
S S
S
signal inputs
March 4, 2008 DF3-15http://csg.csail.mit.edu/arvind/
Procedure Linkage Operatorsf
get frame extract tag
change Tag 0
change Tag 0
Graph for f
change Tag 1
a1
1:
change Tag n
an
n:
...
change Tag 1
Fork
token in frame 0token in frame 1
Like standard call/return but caller & callee can be active simultaneously
March 4, 2008 DF3-16http://csg.csail.mit.edu/arvind/
Unbounded Loop Schema
loop body
X
X
change tag
release context
change tag
• • •
• • •
• • •
T F
p
parentcontext
getcontext
X
••
March 4, 2008 DF3-17http://csg.csail.mit.edu/arvind/
Reusing ContextsCan we tie the allocation of context in iteration i with the release of context in iteration i-k?
Start with k contexts, c0, c1, ... ck-1 Bound the loop so that no more than k iterations can
execute concurrently. At the end of iteration i, use the context from
iteration (i+1) mod k. Release the contexts when the loop terminates
. . . . . ck-1c0 c1
March 4, 2008 DF3-18http://csg.csail.mit.edu/arvind/
Bounded Loops
The parent allocates k frames and stores the linking information and the loop constants.The name of the previous frame and the parent frame is stored in all frames but the next frame slot of the last frame is left empty.When an iteration begins it empties the next slot and when it completes it fills the next slot of the previous frame.
. . .
nextpreviousparentloopconstants
0 1 k-1
March 4, 2008 DF3-19http://csg.csail.mit.edu/arvind/
Unbounded Loop Schema
loop body
X
X
change tag
release context
change tag
• • •
• • •
• • •
T F
p
parentcontext
getcontext
X
••
Bounded
get “next”
extract “context” put “previous”
March 4, 2008 DF3-20http://csg.csail.mit.edu/arvind/
Next: Id/pH to Dataflow Graphs
