BandwidthSaturation

Description

The pattern "Bandwidth Saturation" describes the performance limitation caused by fully utilizing a shared data path. It depends on the system level which data path can be saturated. Inside CPU packages and whole compute nodes, the main resource for saturation is the memory subsystem but also the last level cache is a candidate. At cluster level, the shared data path is the interconnect network shared by all compute nodes.

Symptoms

• Saturating speedup across cores sharing a data path

Detection

At system level use a hardware-counter tool like:

• LIKWID with performance groups MEM and L3
• Same information can be provided by perf or PAPI

At cluster level you need special tools for the specific network technology

Possible optimizations and/or fixes

• Reorganize access to data with methods like spacial or temporal blocking