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 <[email protected]> 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 [email protected]<mailto:[email protected]> 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 <[email protected]<mailto:[email protected]>> wrote: Cool — all seem fixable :-) Anthony Skjellum, PhD 205-807-4968 On May 28, 2019, at 4:25 PM, HOLMES Daniel via mpiwg-persistence <[email protected]<mailto:[email protected]>> 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 [email protected]<mailto:[email protected]> 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 [email protected]<mailto:[email protected]> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-persistence