# 8.5. Multiple levels of interception

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The scheme given here does not directly support the nesting of profiling functions, since it provides only a single alternative name for each MPI function. Consideration was given to an implementation which would allow multiple levels of call interception, however we were unable to construct an implementation of this which did not have the following disadvantages

- assuming a particular implementation language.
- imposing a run time cost even when no profiling was taking place.

Since one of the objectives of MPI is to permit efficient, low latency implementations, and it is not the business of a standard to require a particular implementation language, we decided to accept the scheme outlined above.

Note, however, that it is possible to use the scheme above to implement a multi-level system, since the function called by the user may call many different profiling functions before calling the underlying MPI function.

Unfortunately such an implementation may require more cooperation between the different profiling libraries than is required for the single level implementation detailed above.

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