How to understand uct_iface_attr::latency?

[XCloudAI]

The docucment says Latency as function of number of active endpoints.
What is measured for the latency here?

[yosefe]

Latency is time estimation (in seconds) for time spent in the transport device and network as function of number of active endpoints. Pls see usage example in

ucx/src/ucp/core/ucp_context.h

Line 437 in 55c2885

ucp_tl_iface_latency(ucp_context_h context, const ucs_linear_func_t *latency)

[changchengx]

https://github.com/yosefe/ucx/blob/v1.9.0-pre38/src/uct/ib/base/ib_iface.c#L1303
https://github.com/yosefe/ucx/blob/v1.9.0-pre38/src/uct/ib/base/ib_iface.c#L1370
https://en.wikipedia.org/wiki/InfiniBand

[changchengx]

difference from overhead:
https://github.com/yosefe/ucx/blob/v1.9.0-pre38/src/uct/ib/rc/verbs/rc_verbs_iface.c#L183