Subject: hpff-task: Re: Proposal for task parallelism

From: [email-masked] (Chuck Koelbel)
Date: Thu, 14 Sep 1995 16:56:59 -0500

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At 17:05 09/14/95, [email-masked] wrote:
>>
>> Sounds to me like you're addressing my concerns.  Maybe it would also help
>> to explicitly mention that a processor group always has write access to
>> data mapped to it.
>
>Actually it is mentioned that processor groups have unrestricted access
>to their variables, but only as a comment. Excerpt:
>
>[There are no other access constraints: Code  executing on ALL processors
> has unrestricted  access to all variable locations. A code block directed
> to execute ON a subgroup P has unrestricted access to all variable locations
> mapped to P]
>
>Perhaps it should be in the main text.

I think so.  It's an important point.

>> Also, note that "normal data-parallel mode" on some
>> machines may mean GET/PUT access; copying data in this way in ALL may not
>> be sufficient for the synchronization that you need.
>>
>...
>Anyway, I think this is about efficient  compilation in GET/PUT model
>and I don't think it changes the specification or the basic execution
>model.
>
>jaspal

Agreed.  Is it true that your execution model assumes that the owners of A
and B both participate in A=B (at least in the sense that they do some
synchronization)?  If so, I'd feel better if this were explicitly stated
somewhere.  Yes, in some sense the synchronization is also implied in
straight HPF - but here the model is explicitly multi-threaded, as opposed
to the single-threaded model in HPF-default mode.

                                                Chuck

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---

From: [email-masked]
Date: Fri, 15 Sep 95 10:56:32 -0400

> to the single-threaded model in HPF-default mode.

OK, it will probably make things clearer to state that owners of A
and B both participate in an A=B. But the main point is that execution 
model in ALL is same as regular HPF, (with extra information that subgroup
computations can be assumed to only read and modify subgroup variables
from ALL's perspective), and it should be stated in those 
terms, else we have to detail the behavior in all scenarios. Perhaps
some illustration will make things easier.

jaspal