[libfabric-users] Max IOV length with verbs provider

Carlo Alberto Gottardo carlo.gottardo at cern.ch
Mon Jun 21 06:31:31 PDT 2021

Dear Libfabric developers & users,

using the verbs provider (libfabric v1.12.1), I use the fi_sendmsg to send messages.
The flag FI_INJECT_COMPLETE is used and message I/O vector has a variable length (iov_count).

Independently from the total size of the message, if iov_count > 20 the messages are not sent and EAGAIN is returned.
This means that I can send, for example, 24 kB messages with 3 IOV entries, but not with 24 entries.

To be precise, EAGAIN is returned by ibv_post_send [1] and iov_count is the only parameter that changes in the test.

I understand that multiple causes can underlie an EAGAIN, but given the role of iov_count is there something I can check to start with?

Thank you,

[1] https://github.com/ofiwg/libfabric/blob/v1.12.1/prov/verbs/src/verbs_ep.c#L149

Carlo A. Gottardo
NIKHEF & Radboud U. Nijmegen
32-3-A05, CERN, Meyrin, CH

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