28
The number of cells in a partition should be a power of two, i.e., 2, 4, 8, or 16.
Optimal interleaving of memory across cells requires that the number of cells be a power of two.
Building a partition that does not meet this requirement can create memory regions that are non
optimally interleaved. Applications whose memory pages land in the memory that is interleaved
across just one cell can experience up to 16 times less bandwidth than pages which are
interleaved across all 16 cells.
29
Before consolidating partitions in a Superdome 32-processor or 64-processor system, the
following link load calculation should be performed for each link between crossbars in the
proposed partition.
Links loads less then 1 are best. As the link load begins to approach 2 performance bottlenecks
may occur.
For crossbars X and Y
Link Load = Qx * Qy / Qt / L, where
- Qx is the number of cells connected to crossbar X (quad)
- Qy is the number of cells connected to crossbar Y (quad)
- Qt is the total number of cells in the partition
- L is the number of links between crossbar X and Y (2 for Superdome 32-processor systems and
1 for Superdome 64-processor systems)
30
Maximum performance for optimal configurations is power of two cells, uniform memory across
cells and power of two DIMM ranks per cell.
31
(If rule #30 cannot be met, rule #31 is recommended) Non power of two cells, but still uniform
memory across cells, power of two DIMM ranks per cell, uniform type of DIMM.
32
NOTE:
NOTE:
NOTE:
NOTE: Only Superdome PA-8800 supports 1 GB and 2 GB DIMMs.
(If rule #30 or #31 cannot
be met, rule #32 is recommended) Same amount of memory in each cell, but possibly different
memory types in each cell (for instance, a two cell configuration with 8 512MB DIMMs in one
cell, and 4 1GB DIMMs in the other). Differences in memory across different cells within the same
partition should be minimal for the best performance.
33
NOTE:
NOTE:
NOTE:
NOTE: Only Superdome PA-8800 supports 1 GB and 2 GB DIMMs.
Same amount of memory in
each cell, but non optimal and/or mixed loading within a cell (for instance, a two cell
configuration with 16 512MB DIMMs and 8 1GB DIMMs in each cell).
34
Non-uniform amount of memory across cells (this needs to boot and run, but performance is
whatever you get).
35
Superdome PA-8800 only:
Superdome PA-8800 only:
Superdome PA-8800 only:
Superdome PA-8800 only: For the same amount of total memory, best performance is with a
larger number of smaller size DIMMs.
QuickSpecs
HP 9000 Superdome Servers (PA-8600, PA-8700, PA-
HP 9000 Superdome Servers (PA-8600, PA-8700, PA-
HP 9000 Superdome Servers (PA-8600, PA-8700, PA-
HP 9000 Superdome Servers (PA-8600, PA-8700, PA-
8800 and PA-8900)
8800 and PA-8900)
8800 and PA-8900)
8800 and PA-8900)
System Management Features
DA - 11721 Worldwide — Version 28 — October 23, 2009
Page 39
