README.affinity

CPU affinity is on by default, but depends on the available affinity and
topology libraries. Essentially, the more information available about the
machine, the better decisions can be made about affinity.

The best-supported library is hwloc, which provides a full set of topology
querying and thread- and memory-pinning functions on the widest variety of
platforms, including Linux, BSD, and more. When using hwloc, the default
arrangement is to pin each worker thread to a PU (the lowest level
computational processing unit), and to group them (for the Sherwood scheduler)
by the top-level cache.

Binders is a low level affinity layer for precise control over where workers and
shepherds are allocated. It is implemented as a colon-seperated list of
cpustrings, where each cpustring is a shepherd. It is controlled by the
environment variable QT_CPUBIND. See src/affinity/README.binders for more details.

Unless hwloc is available, worker threads are NOT pinned.

There are several environment variables that can be used to control CPU
affinity and parallelism. See the qthread_initialize() man page for details.