README 1.92 KB
Newer Older
Valentin Reis's avatar
Valentin Reis committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
AML =  Active Messages Library

AML is an SPMD communication library built on top of MPI3 intented to be used in fine grain applications like Graph500

Two main goals of AML : user code clarity while delivering high performance through tricky internal implementation

It's targeted to support asynchronous small messages delivery
while having reasonable performance on modern multicore systems by
doing transparantly to user following

1. message coalescing
2. software routing on multicore systems

To enable both optimizations messages are delivered asynchronously.
To ensure delivery = an completion of handler executions on remote nodes collective barrier should be called.
Current version support only one-sided message (cannot send a response from active message handler)
but future version would support two-sided active messages.

For each process all delivered AMs are executed sequentially, so atomicity is guaranted and no locking required.
Progress of AM delivery is passive which means that handlers are executed inside library calls (aml_send and aml_barrier).

How to send messages:

1. call aml_init(..)

2. register handler of an active message whose prototype should be:
    void handler(int fromPE,void* data,int dataSize)
where fromPE is sender's rank, data is pointer to message sent by sender and dataSize being size in bytes

registration is done using function aml_register_handler( handler, handlerid) where handlerid is integer in range [0..255]

3. send messages to other nodes using 
    aml_send(data,handlerid,dataSize,destPE)
   where data is dataSize bytes of data to be sent to PE with rank destPE and to be processed by handler registered under handlerid

4. call collectively aml_barrier() which would not only synchronize all processes but also ensure that all active messages 
   sent prior to aml_barrier call are delivered (and requested handlers completed its execution) after exit from aml_barrier


5. call aml_finalize()