[mpiwg-persistence] [EXTERNAL] Re: Notes from WG meeting 28th May 2019

Tue May 28 23:09:23 CDT 2019

Hi Ryan,

I noticed some other comments/suggestions not related to your recent feedback changes but I didn’t do a full review of the overall proposal. Most of the comments/suggestions I had on the wider proposal were word-smithing only and could be done between this meeting and the next without derailing the timeline. This means it is definitely worth going through the reading this meeting because it forces a line-by-line review of the whole thing.

Cheers,
Dan.
—
Dr Daniel Holmes PhD
Applications Consultant in HPC Research
d.holmes at epcc.ed.ac.uk<mailto:d.holmes at epcc.ed.ac.uk>
Phone: +44 (0) 131 651 3465
Mobile: +44 (0) 7940 524 088
Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT
—
The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
—

On 28 May 2019, at 22:34, Grant, Ryan Eric (-EXP) <regrant at sandia.gov<mailto:regrant at sandia.gov>> wrote:

Everyone,

Here are the changes based on feedback from today. There are quite a few changes but overall it is far less text than we had before. I'd appreciate any feedback and any other sets of eyes on this for a sanity check.

Thanks,
Ryan
________________________________
From: HOLMES Daniel <d.holmes at epcc.ed.ac.uk<mailto:d.holmes at epcc.ed.ac.uk>>
Sent: Tuesday, May 28, 2019 7:32 PM
To: Anthony Skjellum; Grant, Ryan Eric (-EXP)
Cc: MPI WG Persistence working Group
Subject: [EXTERNAL] Re: [mpiwg-persistence] Notes from WG meeting 28th May 2019

Hi all,

After further discussion, one of the answers has changed.

Question: how does datatype describe complex layouts?
Answer: it does not - it is the same as I/O with eType == xfer_type and fileType == contig

New answer: the {count, datatype} tuple specifies the type map for a single partition; that interpretation of the proposed parameters permits a straightforward generalisation to MPI_Psendv_init and MPI_Psendw_init, which allow the type map to be different for each partition. For MPI_Psendv_init, the count parameter becomes an array of counts (of length equal to the numPartitions parameter) that gives the type map for the Nth partition via an implicit MPI_Type_contiguous(count_array[N], xfer_type) construction. For MPI_Psendw_init, both the count and data type parameters become arrays (of length equal to the numPartitions parameter) that give the type map for the Nth partition via an implicit MPI_Type_contiguous(count_array[N], type_array[N]) construction. The W version would benefit from an additional of displacements for the same reason as for the existing W functions in MPI. These extension functions permit arbitrary partitioning in future but require a change to the proposed special-case functions.

Note: this new interpretation of the existing parameters for MPI_Psend_init and MPI_Precv_init avoids the possibility of the user giving a number of partitions that does not work with the {count, data type} tuple, e.g.
  numPartitions = 3
  count = 10
  datatype = MPI_Type_contiguous(100, MPI_DOUBLE)
With the previous interpretation of the input parameters (i.e. the {count, data type} tuple specifies the type map for all partitions combined), this means MPI must try to divide 1000 doubles into 3 equally sized partitions, which leads to buffer under-run situations or to mandating some input combinations are erroneous.
With the new interpretation of the input parameters (i.e. the {count, data type} tuple specifies the type map for each partition), this means there are 3 partitions of 1000 doubles, i.e. 3000 doubles in total across all partitions.

This is quite a fundamental change for a no-no vote, so it may result in the proposal being read (again) at the next face-to-face meeting.

Cheers,
Dan.
—
Dr Daniel Holmes PhD
Applications Consultant in HPC Research
d.holmes at epcc.ed.ac.uk<mailto:d.holmes at epcc.ed.ac.uk>
Phone: +44 (0) 131 651 3465
Mobile: +44 (0) 7940 524 088
Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT
—
The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
—

On 28 May 2019, at 18:27, Skjellum, Anthony <Tony-Skjellum at utc.edu<mailto:Tony-Skjellum at utc.edu>> wrote:

Cool — all seem fixable :-)

Anthony Skjellum, PhD
205-807-4968

On May 28, 2019, at 4:25 PM, HOLMES Daniel via mpiwg-persistence <mpiwg-persistence at lists.mpi-forum.org<mailto:mpiwg-persistence at lists.mpi-forum.org>> wrote:

Hi Ryan,

Here are my notes from the WG meeting today:

Define channel - for all usages throughout the spec (existing and proposed).

Example: use variables for tag, dest, etc parameters in the Psend_init call
Example: use variables for tag, dest, etc parameters in the Precv_init call

Example: typo for MPI_Pstart - should be MPI_Start and should not end with brace

Example: typo for &xfer_type in the Psend_init call - use just xfer_type instead
Example: typo for &xfer_type in the Precv_init call - use just xfer_type instead
Example: typo for &request and &i in the Pready call - use just request and i instead
Example: typo for &part in the Pwait call - use just part instead

Question: can partitioned receive match with any other send than the partitioned send it matched with during initialisation? No.

Question: how does datatype describe complex layouts?
Answer: it does not - it is the same as I/O with eType == xfer_type and fileType == contig

Suggestion: add an MPI_Info parameter to both MPI_Psend_init and MPI_Precv_init

Example: typo for amp parallel for (the for is missing)

Example: tasks need to use different values for i in Pready

Suggestion: mandate exactly one call to Pready for each partition between start and wait

Suggestion: partition parameters must be consistent - either int or MPI_Count

Note: there is room for (and potential use-cases for) Psendv_init (Pavan’s case) and Psendw_init (Rich’s case)

Cheers,
Dan.
—
Dr Daniel Holmes PhD
Applications Consultant in HPC Research
d.holmes at epcc.ed.ac.uk<mailto:d.holmes at epcc.ed.ac.uk>
Phone: +44 (0) 131 651 3465
Mobile: +44 (0) 7940 524 088
Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT
—
The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
—

_______________________________________________
mpiwg-persistence mailing list
mpiwg-persistence at lists.mpi-forum.org<mailto:mpiwg-persistence at lists.mpi-forum.org>
https://lists.mpi-forum.org/mailman/listinfo/mpiwg-persistence

<part.pdf>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mpi-forum.org/pipermail/mpiwg-persistence/attachments/20190529/8287f24e/attachment-0001.html>