[Mpi3-subsetting] MPI subsetting: charting the way forward atatelecon next week?
Supalov, Alexander
alexander.supalov at [hidden]
Fri Jun 20 12:14:30 CDT 2008
Why make it difficult when an int in the mpi_init call seems to be
sufficient?
-----Original Message-----
From: mpi3-subsetting-bounces_at_[hidden]
[mailto:mpi3-subsetting-bounces_at_[hidden]] On Behalf Of Bronis
R. de Supinski
Sent: Friday, June 20, 2008 7:05 PM
To: MPI 3.0 Sub-setting working group
Subject: Re: [Mpi3-subsetting] MPI subsetting: charting the way forward
atatelecon next week?
Yes, but the best approach would be a query/subscribe
interface, possibly with some set of standard ketwords
that provide portability.
On Fri, 20 Jun 2008, Supalov, Alexander wrote:
> Hi,
>
> Ignoring an assertion should be perfectly legal.
>
> Best regards.
>
> Alexander
>
> ________________________________
>
> From: mpi3-subsetting-bounces_at_[hidden]
> [mailto:mpi3-subsetting-bounces_at_[hidden]] On Behalf Of
> Richard Graham
> Sent: Friday, June 20, 2008 6:53 PM
> To: MPI 3.0 Sub-setting working group
> Subject: Re: [Mpi3-subsetting] MPI subsetting: charting the way
forward
> atatelecon next week?
>
>
> I think we need to be careful here when it comes to assertions, and
> think hard about how
> you want to handle these in a standard. In some of the
implementations
> I am familiar with
> a no-eager-throttle key word would be useless - it is vey
> implementation specific. I suppose
> this is a big problem with trying to add implementation specific
> keywords to a standard.
> It is a given that this will also cause trouble when trying to come
up
> with an ABI, unless
> one has a large set of defined constants, and are willing to have
these
> be no-ops in
> certain implementations.
>
> Rich
>
>
> On 6/20/08 9:56 AM, "Richard Treumann" <treumann_at_[hidden]> wrote:
>
>
>
> Hi Alexander
>
> Comments imbedded below.
>
> I have no objections to someone providing a rationale for
> assertions related to MPI-IO and MPI_1sided. If the rationale is
sound
> I have no objection to putting them in the proposal.
>
> I feel the proposal should be evaluated by the following
> algorithm.
>
> If (this concept is one that seems plausible) {
> for each proposed assertion {
> if (rationale not solid)
> discard
> if (deal breaker downside)
> discard
> }
> if ((concept makes sense) & (set of worthwhile assertions is not
> empty))
> make this part of MPI 2.2
>
> I do not see much reason to get every assertion that eventually
> gains traction into MPI 2.2. MPI 3.0 is soon enough for any that do
not
> make the MPI 2.2 cut. I do not want to see the concept fall because
some
> particular assertion is controversial.
>
> I consider MPI_NO_EAGER_THROTTLE to be the single most valuable
> assertion for MPI 2.2 because it is needed to allow MPI to scale to
the
> levels we are already seeing.
>
>
> 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
>
>
> mpi3-subsetting-bounces_at_[hidden] wrote on 06/20/2008
> 02:58:41 AM:
>
> > Dear Dick,
> >
> > A couple of suggestions re your proposal:
> >
> > - If ASSERTIONS is put at the end of the MPI_INIT_ASSERTED
> argument
> > list, in C++ one can declare the last argument as having a
> zero
> > default value, and skip it if necessary. This might help with
> > deprecation of the earlier MPI_INIT_* calls.
>
> I have no objection. It seems reasonable to let C++ default the
> assertions parameter to "none"
>
> > - In non-Cray parts of the world, an MPI_INT followed by
> MPI_FLOAT
> > is likely to be a 4-byte int followed by a 4-byte float. This
> > sometimes depends on the compiler settings in effect, too.
>
> My rationale is not specific to any particular architecture.
> Some MPI datatypes are made entirely
> from the same base type. Some are mixtures of types. If libmpi
> knows
> at the moment a datatype is committed that the send side and
> receive
> side will always use the same internal representions then it
> does not
> need to keep track of the fact that one instance of
> {MPI_INT,MPI_FLOAT}
> has two distinct parts. The send side can gather and ship 8
> bytes
> and the receive side can scatter the 8 bytes. If one side might
> use 4
> byte integers while the other side uses 8 byte integers then at
> least one side will need to know there is a conversion to be
> done for
> the MPI_INT part. If an MPI job does a spawn or join that links
> to a
> different architecture after the datatype has been committed,
> and
> the MPI_Type_commit has discarded the details, it is too late to
> get
> them back. On the other hand, if it is known there will never
> be a
> different architecture added to the job, the extra information
> can be
> safely discarded.
>
> > - I don't think MPI_NO_THREAD_CONTENTION is really necessary.
> The
> > original thread level settings, in particular, the use of
> anything
> > but MPI_THREAD_MULTIPLE, seem to capture the semantics that
> you proposed.
>
> This one is kind of tricky and I also am not sure what it would
> mean. If
> we find a clear value we can keep it and if not we can remove
> it.
>
> > - I can't fully follow the motivation for MPI_NO_ANY_SOURCE
> > deprioritization. AFAIK, a rendezvous exchange usually starts
> with a
> > ready-to-send packet that contains the size of the message. In
> this
> > case the receiving side will normally reply with a
> ready-to-receive
> > regardless of the buffer space available, and flag
> MPI_ERR_TRUNCATED
> > on message arrival if necessary. In this case, neither
> > MPI_ANY_SOURCE not MPI_NO_ANY_SOURCE seem to get into way.
>
> My point is that MPI_NO_ANY_SOURCE might allow this round trip
> protocol to be replaced by a 1/2 rendezvous protocol. If it is
> known
> that MPI_ANY_SOURCE will not be used then the receive side can
> send
> an "envelop and ready for data" packet to the send side. As long
> as
> the send side knows it will receive the "envelop and ready for
> data"
> packet when the receive is posted, it does not need to do the
> first 1/2
> of the rendezvous. The message matching can be done at the send
> side.
>
> A send for which the receive was preposted has a
> good chance of finding the "envelop and ready for data" sitting
> in
> an early queue and the large send can avoid any rendezvous
> delay.
> Data begins to flow immediately vs waiting for a round trip of a
>
> full rendezvous. In many cases we cut the delay in half and best
>
> case we eliminate rendezvous delay completely. If the receive
> side
> is late in posting the receive we still save a packet traversal
> but
> do not save any time.
>
> If there may be an MPI_ANY_SOURCE then this does not work
> because the
> receive side that has an MPI_ANY_SOURCE cannot guess which
> sender to
> notify so the sender cannot count on getting a 1/2 rendezvous
> notification for a message that should match the MPI_ANY_SOURCE
> receive.
>
> The problem that made me lower the priority is that many MPIs
> use an
> eager protocol for small messages and a rendezvous protocol for
> large
> messages. If the send side and receive side have the same size
> buffer
> then both sides can reach the same conclusion: eager vs 1/2
> rendezvous.
> If both decide on eager, the receive side will not send an
> "envelop and ready for data" packet and the send side will not
> look
> for one. If both sides decide on 1/2 rendezvous then the receive
> side
> will send an "envelop and ready for data" packet and the send
> side will
> look for and consume the notice. If the send side is for an 8
> byte
> message and the receive uses a "big enough" receive buffer of
> 64KB
> then the two sides will probably not be able to reach the same
> conclusion about the protocol. The receive side will ship off an
> "envelop and ready for data" packet that the send side will not
> know what to do with.
>
>
> >
> > Best regards.
> >
> > Alexander
> >
> > From: Supalov, Alexander
> > Sent: Friday, June 20, 2008 8:29 AM
> > To: 'MPI 3.0 Sub-setting working group'
> > Subject: RE: [Mpi3-subsetting] MPI subsetting: charting the
> way
> > forward at atelecon next week?
>
> > Dear Dick,
> >
> > Thank you. I remember we exchanged a couple of emails about
> the
> > possible extensions to the set of assertions, like one-sided
> and
> > I/O, and in my recollection, almost reached an agreement that
> this
> > can improve performance and possibly memory footprint, as well
> as be
> > expressed thru assertions. Do you still feel favorable about
> this?
> >
> > Best regards.
> >
> > Alexander
> >
>
>
>
> ________________________________
>
> _______________________________________________
> mpi3-subsetting mailing list
> mpi3-subsetting_at_[hidden]
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-subsetting
>
>
>
>
> ---------------------------------------------------------------------
> Intel GmbH
> Dornacher Strasse 1
> 85622 Feldkirchen/Muenchen Germany
> Sitz der Gesellschaft: Feldkirchen bei Muenchen
> Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer
> Registergericht: Muenchen HRB 47456 Ust.-IdNr.
> VAT Registration No.: DE129385895
> Citibank Frankfurt (BLZ 502 109 00) 600119052
>
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.
>
_______________________________________________
mpi3-subsetting mailing list
mpi3-subsetting_at_[hidden]
http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-subsetting
---------------------------------------------------------------------
Intel GmbH
Dornacher Strasse 1
85622 Feldkirchen/Muenchen Germany
Sitz der Gesellschaft: Feldkirchen bei Muenchen
Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer
Registergericht: Muenchen HRB 47456 Ust.-IdNr.
VAT Registration No.: DE129385895
Citibank Frankfurt (BLZ 502 109 00) 600119052
This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.
More information about the Mpi3-subsetting
mailing list