Common OFI Mistakes to Avoid
Erik Paulson edited this page Oct 11, 2017
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This document is meant to document or highlight commonly misunderstood aspects of the OFI documentation in order to help application developers avoid potential problems. This should not be taken as a substitute for a thorough reading of the manpages.
- All endpoints that issue asynchronous operations must be bound to a relevant CQ, even if they don't report completions.
- This is for error reporting purposes. Take for example an endpoint configured with FI_SELECTIVE_COMPLETION and bound to a counter, which only reads from the counter. If the counter read returns an error, the application may then read a more detailed error entry from the completion queue.
- The endpoint needs only to be bound to a CQ for the operation types it will initiate. For example, if an endpoint will only issue receive operations, it only needs to be bound to a CQ using the FI_RECV flag.
- When the FI_CONTEXT (or FI_CONTEXT2) mode bit is specified, the application must pass in a valid 'struct fi_context' (or struct fi_context2) when initiating an operation, such as send/recv/rma write. The memory pointed to by the structure needs to remain valid during the entire duration of the operation, until a valid completion is received by the application by reading the completion queue. Additionally, no other operation may reuse the struct fi_context during the time the original operation is outstanding. If the application erroneously reuses the struct fi_context, or erroneously reuses the context, an undefined error might occur. In some cases the error might appear as stack corruption which can be hard to debug!
- The exception to this rule is when FI_SELECTIVE_COMPLETION is enabled to suppress completion entries, and an operation is initiated without FI_COMPLETION flag set, the context parameter is ignored.