Editing Vector processor (section)

== Performance and speed up ==

Let '''''r''''' be the vector speed ratio and '''''f''''' be the vectorization ratio. If the time taken for the vector unit to add an array of 64 numbers is 10 times faster than its equivalent scalar counterpart, r = 10. Also, if the total number of operations in a program is 100, out of which only 10 are scalar (after vectorization), then f = 0.9, i.e., 90% of the work is done by the vector unit. It follows the achievable speed up of:

<math>r/[(1-f)*r+f]</math>

So, even if the performance of the vector unit is very high (<math>r=\infty</math>) there is a speedup less than <math>1/(1-f)</math>, which suggests that the ratio '''''f''''' is crucial to the performance. This ratio depends on the efficiency of the compilation like adjacency of the elements in memory.