[Omp] Re: [General] schedule(static)

[Cos Ierotheou]

Dear Mark,
I agree with Dieter. Specifically on the issue and solution he proposes (see extract from 
previous email below). It is essential that as much ambiguity is removed from the SPEC and 
this is a good example to highlight the dangers of not doing so. This is not only 
ambiguous to the compiler writers but also to the code developers - the people that 
matter! In this case, I suspect (and to some degree hope) that many people interpreted the 
meaning in the same way that Dieter has, nonetheless, in my opinion a change in the text 
is necessary to remove any ambiguity and make this explicit.

Cos.


Dieter an Mey wrote:
>> The problem is the nowait clause. The draft V2.5 specs say on page 34 
>> line 11-18:
>>
>> "When schedule(static, chunk_size) is specified, iterations are divided
>> into chunks of size chunk_size, and the chunks are statically assigned 
>> to threads in the team in a round-robin fashion in the order of the 
>> thread number.
>> Note that the last chunk to be assigned may have a smaller number of
>> iterations.
>> When no chunk_size is specified, the iteration space is divided into 
>> chunks which are approximately equal in size, and such that each 
>> thread is assigned at most one chunk."
>>
>> The interpretation is that if the chunk_size would specified, the work 
>> distribution is unambiguously defined and the nowait clause would be ok.
>>
...
>> I suggest that the specs should be modified and that for a fixed 
>> number of threads and a fixed number of iterations an identical 
>> schedule should be used, even if the chunk_size is not specified 
>> explicitely.
>>
>> I think that this difference between a static schedule with and 
>> without an explicitely specified chunk_size is very misleading and 
>> dangerous.
>>


-- 
Dr. Constantinos Ierotheou,
Parallel Software Products,
Tel: +44 (020) 8331-8655
Fax: +44 (020) 8331-8665
http://www.parallelsp.com

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