Performance tunning

LCI communication backend

Registration Cache

LCI needs to register the user-provided buffers when sending large messages (messages larger than the eager protocol threshold). It will incur a per-message overhead of usually tens of microseconds. Registration cache can help LCI reduce registration overhead at the price of increased threading content in the cache.

The registration cache is not enabled by default in LCI. To enable it in Charm, specify the following argument when building Charm.

./build ... --with-cmake-args=-DLCI_USE_REG_CACHE=ON

Note: it cannot be enabled on APPLE devices.

Once the registration cache is enabled during the build time, it will be automatically used during the runtime. You can still turn it off by

export LCI_ATTR_USE_REG_CACHE=OFF