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On Sun, Apr 27, 2025 at 7: 04 PM Skjellum, Anthony <askjellum@ tntech. edu> wrote: Jeff, thank you, I will read more about UCC. In the meantime, since I like MPI a lot, and intend to keep using it, and trying to make it better, I mentioned</div>
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<div dir="ltr"><div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Sun, Apr 27, 2025 at 7:04 PM Skjellum, Anthony <<a href="mailto:askjellum@tntech.edu">askjellum@tntech.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913">
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Jeff, thank you, I will read more about UCC. </div>
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In the meantime, since I like MPI a lot, and intend to keep using it, and trying to make it better, I mentioned this because I view MPI_Info arguments is a substitute for polymorphism in the interface, as I know you know, and with AI/machine-learning, we might
be able to generate wisdom/profile-guided optimization to fulfill these arguments. Is this not a good direction?</div></div></div></blockquote><div><br></div><div>If somebody wants to do this, they can implement it on a per call site inside of the MPI library by running a short backtrace to identify the call site and selecting an algorithm for that call site based on a profile database.</div><div><br></div><div>On the other hand, nobody cares if it's MPI or not when the standard API of interest to AI is pytorch.distributed.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913"><div dir="ltr"><div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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And, since you probably know that I've brought up orthogonality of the APIs before many times in the meetings, I am worried that we have not made the more general operations like non-blocking have the ability to give assertions or info. </div></div></div></blockquote><div><br></div><div>I would pay money for you and Jasper to have a public debate about adding versus subtracting features from MPI ;-) </div><div><a href="https://urldefense.us/v3/__https://github.com/mpi-forum/mpi-issues/issues/976__;!!G_uCfscf7eWS!aXpTAb398eygn3IYLShWbw0TYw6bcAKYcdlRCrUZJxQ2At1MnpGDXlAa5rZ2ZlCgmnCSchE8HwAYq6tCIuHdk1RpDktcpQLzmvBA$">https://github.com/mpi-forum/mpi-issues/issues/976</a></div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913"><div dir="ltr"><div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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I am mostly interested in more performance in MPI, that's why I added my comment to yours. Do you think it is not a good idea to orthogonalize to support optimization, or is there a better way to achieve higher performance in your opinion. </div></div></div></blockquote><div><br></div><div>No, I don't care about orthogonality and I don't prioritize peak performance.</div><div><br></div><div>If we want orthogonality, we should have put, put-with-notify, wait and test, and implement everything else in terms of those. We are so far from orthogonality and it's fine. We have 5+ kinds of send. We can implement alltoall with scatter or with send-recv or with win_create+fence+put, etc. etc. The MPI standard has so much linear dependency and that's actually fine, because it's solving the problems that our users have.</div><div><br></div><div>See the following comment about peak performance...</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913"><div dir="ltr"><div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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Right now, MPI is slower than vendor-specific primitives, limiting its use on key applications. That also drives my thinking.</div></div></div></blockquote><div><br></div><div>And this has always been true. It was true on Blue Gene, yet only the QCD folks wrote in anything but MPI. I regularly gave workshop talks about the merits of DCMF and PAMI, but nobody used them for anything except implementing GASNet and Charm++.</div><div><br></div><div>I don't think peak performance is feasible for MPI and don't think it's a useful goal for the Forum. What we want is time- and system-averaged performance over all the HPC architectures across decades.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913"><div dir="ltr"><div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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The use case I am thinking of is improved choice of algorithm, for collectives. Or knowing that buffers have specific semantics without the cost of testing. </div></div></div></blockquote><div><br></div><div>Yes, allowing expert users to select the algorithm for each call site will show upside in some cases. On the other hand, it will ruin the performance portability of MPI apps, because the best collective algorithm is machine-dependent. At that point, you should just write non-portable code, e.g. UCC. Heck, selecting the best algorithm is not even performance portable across different versions of an MPI library on the same system.</div><div><br></div><div>jeff</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5832572741611485913"><div dir="ltr"><div style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
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Tony</div>
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<div id="m_-5832572741611485913divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Jeff Hammond <<a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a>><br>
<b>Sent:</b> Sunday, April 27, 2025 8:33 AM<br>
<b>To:</b> Skjellum, Anthony <<a href="mailto:askjellum@tntech.edu" target="_blank">askjellum@tntech.edu</a>><br>
<b>Cc:</b> <a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a> <<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a>><br>
<b>Subject:</b> Re: [mpiwg-languages] static datatypes lifetimes</font>
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<div dir="ltr">I think the API you want then is basically UCC. Prescribe everything for every operation.
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<div dir="ltr">On Sun, Apr 27, 2025 at 6:10 PM Skjellum, Anthony <<a href="mailto:askjellum@tntech.edu" target="_blank">askjellum@tntech.edu</a>> wrote:<br>
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Another issue: Info arguments are missing on non-blocking and blocking collectives.</div>
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<div id="m_-5832572741611485913x_m_1114522221898429875divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> mpiwg-languages <<a href="mailto:mpiwg-languages-bounces@lists.mpi-forum.org" target="_blank">mpiwg-languages-bounces@lists.mpi-forum.org</a>>
on behalf of Jeff Hammond via mpiwg-languages <<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a>><br>
<b>Sent:</b> Saturday, April 26, 2025 11:53 PM<br>
<b>To:</b> <a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a> <<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a>><br>
<b>Cc:</b> Jeff Hammond <<a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a>>;
<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a> <<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a>><br>
<b>Subject:</b> Re: [mpiwg-languages] static datatypes lifetimes</font>
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Attributes on ops, datatypes and files is critical for multiple use cases. It’s ridiculous we don’t have them. The standard is inconsistent without. Jeff Sent from my iPhone On 27. Apr 2025, at 5. 51, Joseph Schuchart via mpiwg-languages <mpiwg-languages@ lists. mpi-forum. org></div>
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Attributes on ops, datatypes and files is critical for multiple use cases. It’s ridiculous we don’t have them. The standard is inconsistent without.
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<blockquote type="cite">On 27. Apr 2025, at 5.51, Joseph Schuchart via mpiwg-languages <<a href="mailto:mpiwg-languages@lists.mpi-forum.org" target="_blank">mpiwg-languages@lists.mpi-forum.org</a>> wrote:<br>
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Unfortunately, there is a catch: MPI_COMM_SELF is only relevant/available/valid in the World Process Model (WPM), i. e. , if using `MPI_Init`/`MPI_Finalize`. In the Sessions process model, predefined communicators are not available. The life-time</div>
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<pre style="font-family:sans-serif;font-size:100%;white-space:pre-wrap">Unfortunately, there is a catch: MPI_COMM_SELF is only
relevant/available/valid in the World Process Model (WPM), i.e., if
using `MPI_Init`/`MPI_Finalize`. In the Sessions process model,
predefined communicators are not available.
The life-time of datatypes is a known quirk and I think it was
discovered after Sessions became part of the standard. They are not
bound to any other MPI object and can survive complete shutdown of all
sessions / the WPM. IIRC in Open MPI (but have to check), datatypes
retain a reference on the internal MPI instance and it is the
application's responsibility to free all MPI objects before shutdown.
Once the last datatype/session/wpm is gone we release the instance.
I don't like the state of things there and it is problematic. For
starters, it prevents complete session isolation (and the benefits that
come with it, such as different threading levels). It's not clear to me
how that can be rectified and I think the Forum is not clear on that
either, which is why we ended up with this weird zombie state. If
someone wants to open a ticket to start a discussion on this I'm happy
to participate.
For the problem at hand though (as I understand it), maybe it's
sufficient to add attributes to datatypes? I don't see why that would be
a problem and if it helps with language adoption we have a good argument
for it.
Cheers
Joseph
On 4/25/25 17:24, Alfredo Correa via mpiwg-languages wrote:
> Hi Sayan, On Fri, Apr 25, 2025 at 2: 03 PM Ghosh, Sayan
> <sayan. ghosh@ pnnl. gov> wrote: Consider finalize-delete-callback
> (this is what Alfredo is alluding to perhaps w. r. t
> datatype-attached-to-environment) – that seems to rely on MPI_COMM_SELF
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> Hi Sayan,
>
> On Fri, Apr 25, 2025 at 2:03 PM Ghosh, Sayan <<a href="mailto:sayan.ghosh@pnnl.gov" target="_blank">sayan.ghosh@pnnl.gov</a>> wrote:
>
> * Consider finalize-delete-callback (this is what Alfredo is
> alluding to perhaps w.r.t datatype-attached-to-environment) –
> that seems to rely on MPI_COMM_SELF callback (freeing
> comm-self triggers callback)
>
>
>
> That is a good point. At first glance, attaching things to
> MPI_COMM_WORLD or MPI_COMM_SELF would have a similar effect to
> attaching stuff to the environment.
> I didn't think about this because I was reluctant to modify (in any
> way) either of these special communicators, in particular MPI_COMM_WORLD.
> But MPI_COMM_SELF might still be a good candidate; others can point
> out if there is a catch.
>
> Thanks,
> Alfredo
> _
> _
>
>
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<div dir="ltr">Jeff Hammond<br>
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</div></blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature">Jeff Hammond<br><a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a><br><a href="https://urldefense.us/v3/__http://jeffhammond.github.io/__;!!G_uCfscf7eWS!aXpTAb398eygn3IYLShWbw0TYw6bcAKYcdlRCrUZJxQ2At1MnpGDXlAa5rZ2ZlCgmnCSchE8HwAYq6tCIuHdk1RpDktcpRiJG0ch$" target="_blank">http://jeffhammond.github.io/</a></div></div>