[Mpi-22] MPI_INIT assertions
Terry Jones
trj at [hidden]
Tue May 13 17:19:07 CDT 2008
The Assertions idea has much to offer. The pre MPI_Init case seems to
be a clear winner, but can we generalize Assertions a little more
without too heavy a cost?
I would like to see Assertions extended to permit the application
developer to provide additional context *during* the application run.
Many MPI implementations have a whole laundry list of environment
variables, but long running applications can go through several
phases and a single value of a critically important environment
variable may not make much sense. Perhaps Assertions could be used to
change these type of tunables dynamically during the application.
You can also imagine other possibilities to provide helpful context.
For instance, perhaps the user could provide Assertions that would
help MPI IO with read-ahead prefetching or write-behind, or even
meta-data operations (e.g., later I will be creating one file per MPI
task).
Regards,
Terry
At 5:53 PM -0400 5/5/08, Richard Treumann wrote:
>I changed the subject to be meaningful - it had been "Re: [Mpi-22]
>mpi-22 Digest, Vol 2, Issue 7"
>
>I do think this proposal is within the scope of the MPI 2.2 rules so
>I am pleased to hear this is being considered.
>
>I am 100% convinced that a query function should be part of this
>proposal, probably with 2 query flavors. One flavor of the query
>would respond with the set of assertions the application
>MPI_INIT_xxx call had provided and another would respond with the
>set of assertions the MPI implementation is actually exploiting.
>
>One library author may decide he will use if/else logic based on how
>the MPI implementation will behave. The application may assert
>MPI_NO_yyy but if the MPI implementation does not exploit MPI_NO_yyy
>then the library can still use the code that depends on yyy. Another
>library author may depend unconditionally on yyy. On an MPI
>implementation that does not exploit MPI_NO_yyy he may want to issue
>a warning that assertion MPI_NO_yyy is non-portable but let the job
>run. On one that does exploit MPI_NO_yyy he would abort the job. Or,
>he may decide to simply abort any job that asserts MPI_NO_yyy to
>avoid having the library suddenly quit working when the customer
>upgrades to an MPI implementation that does exploit MPI_NO_yyy.
>
>I think 32 assertions is probably more than enough
>
>Even a handful of defined assertions can raise testing costs. For
>simple cases like MPI_NO_ANY_SOURCE it is easy for a user to judge
>whether a piece of code is OK but if we begin to add subtle or
>narrow semantic assertions it gets harder. Some library providers
>will be tempted to say "I cannot proof read and test my code to a
>degree that will allow me to accept 28 specific assertions and
>forbid 4. I will simply forbid every subtle assertion I cannot
>afford to test."
>
>I predict that for large applications developed by teams and for
>community open source efforts the design leads will consider
>requiring that all parts be written to live within a few carefully
>chosen assertions. The design leads will not want to provide a list
>of 26 subtle or narrow assertions and require that everyone respect
>all 26 in the code they contribute.
>
>Many distinct assertions also could become a big test cost for MPI
>implementors and customers who must qualify an MPI implementation
>before trusting their business to it. If there were 64 or more
>assertions, how would a tester decide what combinations of
>assertions must be tested and then create suitable test cases?
>
>Dick
>
>Dick Treumann - MPI Team/TCEM
>IBM Systems & Technology Group
>Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
>Tele (845) 433-7846 Fax (845) 433-8363
>
>
>mpi-22-bounces_at_[hidden] wrote on 05/05/2008 01:28:06 PM:
>
>> Dear Dick,
>>
>> Thank you. We can actually introduce what you propose, possibly with
>> a query function to make it still easier to live with, as early as
>> in MPI 2.2, as a subset precursor. Judging by the discussion in
>> Chicago, subsets may not need much more than that in the end,
> > possibly with a little more flags and semantics added in MPI-3.
>>
>> The reservation against 32- (or for that matter, 64-) bit limitation
>> is the only one I have at the moment. Not being able to attach
>> assertions to communicators, etc. may be missed by some advanced
>> programmers, but here we need to be pragmatic: who will ever want to
>> go that deep?
>>
>> Best regards.
>>
>> Alexander
>>
>> From: mpi-22-bounces_at_[hidden] [<mailto:mpi-22->mailto:mpi-22-
>> bounces_at_[hidden]] On Behalf Of Richard Treumann
>> Sent: Monday, May 05, 2008 7:18 PM
>> To: MPI 2.2
>> Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7
>
>> Hi Alexander
>>
>> I have no objection to citing my "assertions" proposal in the
>> subsetting discussions. I do want to keep it clear that this
>> proposal is intended to be as simple as practical to implement, exploit and
>> live with.
>>
>> "Live with" applies to 3rd party library authors or anyone else who
>> must write MPI code but does not know and control the structure of
>> the entire application. That guy must "live with" the decisions made
>> by whoever coded the MPI_INIT piece. "Live with" also applies to
>> whoever must test or certify a specific MPI implementation.
>>
>> Thanks - Dick
>>
>> Dick Treumann - MPI Team/TCEM
>> IBM Systems & Technology Group
>> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
>> Tele (845) 433-7846 Fax (845) 433-8363
>>
>> [image removed] "Supalov, Alexander" <alexander.supalov_at_[hidden]>
>>
>
>>
>> "Supalov, Alexander" <alexander.supalov_at_[hidden]>
>> Sent by: mpi-22-bounces_at_[hidden]
>> 04/26/2008 04:03 AM
>>
>> Please respond to
>> "MPI 2.2" <mpi-22_at_[hidden]>
>>
>> [image removed]
>> To
>>
>> [image removed]
>> "MPI 2.2" <mpi-22_at_[hidden]>
>>
>> [image removed]
>> cc
>>
>> [image removed]
>>
>> [image removed]
>> Subject
>>
>> [image removed]
>> Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7
>>
>> [image removed]
>>
>> [image removed]
>>
>>
>> Dear Dick,
>>
>> Thank you. Would you mind if I cite your proposal in the subsets
>> discussion? Yours looks like a good alternative to the thinking of
>> some of us that subsets might be very rich and mutable, and to
>> Jeff's proposal on hints I've already cited there with his permission.
>>
>> Best regards.
>>
>> Alexander
>>
>> From: mpi-22-bounces_at_[hidden] [<mailto:mpi-22->mailto:mpi-22-
>> bounces_at_[hidden]] On Behalf Of Richard Treumann
>> Sent: Thursday, April 24, 2008 6:16 PM
>> To: MPI 2.2
>> Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7
>> Dick Treumann - MPI Team/TCEM
>> IBM Systems & Technology Group
>> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
>> Tele (845) 433-7846 Fax (845) 433-8363
>>
>>
>> mpi-22-bounces_at_[hidden] wrote on 04/24/2008 11:33:42 AM:
>>
>> > Hi,
>> >
>> > Note that this is an argument for making the assertions optional: those
>> > who don't care don't have to use them. Those who care should use them
>> > correctly or else. As usual.
>> >
>> > Best regards.
>> >
>> > Alexander
>> >
>>
>> Hi Alexander
>>
>> The assertions are optional in this proposal. If this is added to
>> the MPI standard the minimal impacts (day one impacts) are:
>>
>> ==
>> To application writers (none) - MPI_INIT and MPI_INIT_THREAD still
>> work. MPI_INIT_THREAD_xxx can be
>> passed 0 (zero) as the assertions bit vector.
>>
>> To MPI Implementors (small) - subroutine MPI_INIT_THREAD_xxx can be
>> a clone of MPI_INIT_THREAD under the covers. If the Forum decides
>> the query function is for asking what assertions are being honored,
>> the implementation can just return "none" to every query. If there
>> is also a query for what assertions have been made then there are a
>> few more lines of code the implementor must write to preserve the
>> value so it can be returned(maybe 10 lines)
>>
>> Writers of opaque libraries (small) - call the query function at
>> library init time and if any assertions are found, issue an error
>> message and kill the job. This is awkward for a library that wants
>> to support every MPI whether it has implemented the new query
>>function or not.
>> ==
>>
>> As MPI implementations begin to take advantage of assertions there
> > is more work for the MPI implementor and the library author must
>> begin to think about whether his customer will be upset if the
>> library simply outlaws all assertions.
>>
>> The library author will never be wrong if he simply forbids
>> assertions forever. If they become valuable he will feel the
>> pressure to work it out.
>>
>> The MPI implementor will never be wrong if he adds the API but
>> simply ignores assertions forever. If they become valuable he will
>> feel the pressure to honor some at least.
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