Performance evaluation and cache analysis of an ILP protocol implementation

Integrated layer processing (ILP) is an implementation concept that "permits the implementor the option of performing all the (data) manipulation steps in one or two integrated processing loops". To estimate the achievable benefits of ILP, a file transfer application with an encryption function on top of a user-level TCP has been implemented and the performance of the application in terms of throughput and packet processing times has been measured. The results show that it is possible to obtain performance benefits by integrating marshalling, encryption, and TCP checksum calculation. The experiments yielded in a throughput gain of only 10-20% in contrast to the 50% gain achieved for simple loop experiments. Simulations of memory access and cache hit rate show that the main benefit of ILP is reduced memory access rather than an improved cache hit rate. ILP reduced the number of memory accesses up to 30% in the experiment, but the relative amount of cache misses could not be reduced compared to a carefully designed non-ILP implementation. The results also show that data manipulation characteristics may significantly influence the cache behavior and the achievable performance gain of ILP. Considering these results, ILP can only be recommended in cases where the the ILP loop consists of several, but very simple data manipulations without complex calculations over the data.