From 11921d5eaa82d1786a242d24c4cd7c5fa7a7d246 Mon Sep 17 00:00:00 2001
From: "Peter W. Draper" <p.w.draper@durham.ac.uk>
Date: Wed, 29 Jan 2020 12:30:58 +0000
Subject: [PATCH] Change the default initial partition to edgememory
---
.../ParameterFiles/parameter_description.rst | 30 ++++++++++++-------
src/partition.c | 2 +-
2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/doc/RTD/source/ParameterFiles/parameter_description.rst b/doc/RTD/source/ParameterFiles/parameter_description.rst
index 726631b7e0..4abe0bf913 100644
--- a/doc/RTD/source/ParameterFiles/parameter_description.rst
+++ b/doc/RTD/source/ParameterFiles/parameter_description.rst
@@ -986,26 +986,34 @@ should contain. The type of partitioning attempted is controlled by the::
DomainDecomposition:
initial_type:
-parameter. Which can have the values *memory*, *region*, *grid* or
+parameter. Which can have the values *memory*, *edgememory*, *region*, *grid* or
*vectorized*:
+ * *edgememory*
+
+ This is the default if METIS or ParMETIS is available. It performs a
+ partition based on the memory use of all the particles in each cell.
+ The total memory per cell is used to weight the cell vertex and all the
+ associated edges. This attempts to equalize the memory used by all the
+ ranks but with some consideration given to the need to not cut dense
+ regions (by also minimizing the edge cut). How successful this
+ attempt is depends on the granularity of cells and particles and the
+ number of ranks, clearly if most of the particles are in one cell, or a
+ small region of the volume, balance is impossible or difficult. Having
+ more top-level cells makes it easier to calculate a good distribution
+ (but this comes at the cost of greater overheads).
* *memory*
- This is the default if METIS or ParMETIS is available. It performs a
- partition based on the memory use of all the particles in each cell,
- attempting to equalize the memory used by all the ranks.
- How successful this attempt is depends on the granularity of cells and particles
- and the number of ranks, clearly if most of the particles are in one cell,
- or a small region of the volume, balance is impossible or
- difficult. Having more top-level cells makes it easier to calculate a
- good distribution (but this comes at the cost of greater overheads).
+ This is like *edgememory*, but doesn't include any edge weights, it should
+ balance the particle memory use per rank more exactly (but note effects
+ like the numbers of cells per rank will also have an effect, as that
+ changes the need for foreign cells).
* *region*
The one other METIS/ParMETIS option is "region". This attempts to assign equal
- numbers of cells to each rank, with the surface area of the regions minimised
- (so we get blobs, rather than rectangular volumes of cells).
+ numbers of cells to each rank, with the surface area of the regions minimised.
If ParMETIS and METIS are not available two other options are possible, but
will give a poorer partition:
diff --git a/src/partition.c b/src/partition.c
index e92f98993e..b03d23c158 100644
--- a/src/partition.c
+++ b/src/partition.c
@@ -2054,7 +2054,7 @@ void partition_init(struct partition *partition,
/* Defaults make use of METIS if available */
#if defined(HAVE_METIS) || defined(HAVE_PARMETIS)
const char *default_repart = "fullcosts";
- const char *default_part = "memory";
+ const char *default_part = "edgememory";
#else
const char *default_repart = "none";
const char *default_part = "grid";
--
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