Enforce In-order Execution of I/O

Enforce In-order Execution of I/O (EIEIO) is an assembly language instruction used on the PowerPC central processing unit (CPU) which prevents one memory or input/output (I/O) operation from starting until the previous memory or I/O operation completed. This instruction is needed as I/O controllers on the system bus require that accesses follow a particular order, while the CPU reorders accesses to optimize memory bandwidth usage. ^[1]

Where the name comes from

Notice the pun in the name; the old children's song goes "Old MacDonald had a farm, E-I-E-I-O!". In the book Expert C Programming, Peter van der Linden comments that this instruction is "Probably designed by some old farmer named McDonald" and "There’s nothing wrong with well-placed whimsy."^[2]

References

1. "Help - AIX 6.1 Information Center". Archived from the original on 2013-06-29. Retrieved 2013-06-04.
2. Linden, Peter van der. Expert C Programming: Deep C Secrets (Prentice Hall, 1994) pg.xxii

External links

• PowerPC Architecture Book version 2.2