General comments for Level 1 optimization

All Level 1 optimizations are carried on in the BLDdir/tune/blas/level1 directory and its subdirectories. Under this directory are subdirs with names corresponding to the generic name of the routine in question (eg. AXPY, IAMAX, DOT, etc). It is in these subdirs that the user should place the routines to test and time.

A great deal of the performance win to be had on the Level 1 BLAS, particularly for long vectors, comes from using data prefetch. ATLAS now includes a prefetch header file (described in Section 6.1), which makes prefetch instructions for various systems available for C programmers.