BlockCycDist¶
Usage
use BlockCycDist;
or
import BlockCycDist;
- class BlockCyclic¶
This Block-Cyclic distribution maps maps blocks of indices to locales in a round-robin pattern according to a given block size and start index.
Formally, consider a Block-Cyclic distribution with:
rank
d
start index
(s_1, ...., s_d)
block size
(b_1, ...., b_d)
over locales
targetLocales: [0..N_1-1, ...., 0..N_d-1] locale
It maps an index
(i_1, ...., i_d)
to the localetargetLocales[j_1, ...., j_d]
where, for eachk
in1..d
, we have:j_k = ( (i_k - s_k) / b_k ) (mod N_k)
Limitations
This distribution is work in progress and so has significant limitations.
It has not been tuned for performance.
The only
idxType
currently supported is int or int(64).Example
The following code declares a domain
D
distributed over a Block-Cyclic distribution with a start index of(1,1)
and a block size of(2,3)
, and declares an arrayA
over that domain. The forall loop sets each array element to the ID of the locale to which it is mapped.use BlockCycDist; const Space = {1..8, 1..8}; const D: domain(2) dmapped BlockCyclic(startIdx=Space.lowBound,blocksize=(2,3)) = Space; var A: [D] int; forall a in A do a = a.locale.id; writeln(A);
When run on 6 locales, the output is:
0 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0 2 2 2 3 3 3 2 2 2 2 2 3 3 3 2 2 4 4 4 5 5 5 4 4 4 4 4 5 5 5 4 4 0 0 0 1 1 1 0 0 0 0 0 1 1 1 0 0
Initializer Arguments
The
BlockCyclic
class initializer is defined as follows:proc BlockCyclic.init( startIdx, blocksize, targetLocales: [] locale = Locales, dataParTasksPerLocale = // value of dataParTasksPerLocale config const param rank: int = // inferred from startIdx argument, type idxType = // inferred from startIdx argument )
The argument
startIdx
is a tuple of integers defining an index that will be distributed to the first locale intargetLocales
. For a single dimensional distributionstartIdx
can be an integer or a tuple with a single element.The argument
blocksize
is a tuple of integers defining the block size of indices that will be used in dealing out indices to the locales. For a single dimensional distributionblocksize
can be an integer or a tuple with a single element.The argument
targetLocales
is an array containing the target locales to which this distribution maps indices and data. The rank oftargetLocales
must match the rank of the distribution, or be one. If the rank oftargetLocales
is one, a greedy heuristic is used to reshape the array of target locales so that it matches the rank of the distribution and each dimension contains an approximately equal number of indices.The argument
dataParTasksPerLocale
determines the maximum number of tasks on each Locale for data parallelism.The
rank
andidxType
arguments are inferred from thestartIdx
argument unless explicitly set. They must match the rank and index type of the domains “dmapped” using that BlockCyclic instance.Data-Parallel Iteration
A forall loop over a Cyclic-distributed domain or array executes each iteration on the locale where that iteration’s index is mapped to.