Reproducible Timings?
Origin2000 is shared system ñ by default:
- might share processors with processes from other users;
- might share memory on a node with other processes;
- code might migrate to other processors;
- data might migrate to other processors.
=> difficult to obtain reproducible timings on heavily loaded system.
Graham Riley/Mark Bull (CNC) devised a mechanism for ënailingí processors.
Now ñ SGI provide facility, miser, to guarantee exclusive access to processors, but not to memory.
- The best mechanism available for reproducible timings on a production system.
Notes:
- Best method is to have exclusive access to system.
- Next best is to use cpu sets (?), but this requires root access to organise and is not suitable in a production environment