Sounding out OS noise
Posted November 18, 2008
A doorbell’s chime, a telephone’s ring, a teapot’s scream: Momentary interruptions that jar the mind are the bane of deep thinkers everywhere. Famously focused Wernher von Braun dealt with distraction by clearing his mind of “the unimportant things,” a niece of his recalled.
But computers can’t eliminate the unimportant things, and for the deepest-thinking among them – the high-performance variety – routine distractions known as “operating system (OS) interference” can profoundly reduce speed, accuracy and reliability.
Common to all computers, OS interference, or “noise,” describes background activities, like checking for e-mail or reading a keystroke, that briefly interrupt important tasks at hand.
“OS noise is any interruption of a running program by the operating system,” says Al Geist, computer science research group leader at Oak Ridge National Laboratory (ORNL). “On supercomputers, the OS does many things, like managing the memory used by an application.”
OS noise can’t be eliminated but it can be mitigated, as a new study from Sandia National Laboratory’s Scalable System Software group suggests.
University of New Mexico (UNM) computer science graduate student Kurt Ferreira, his professor-mentor Patrick Bridges and Sandia team leader Ron Brightwell propose “decomposing periodic services into smaller pieces that run more often” to reduce the impact of noise on application performance in large-scale, parallel systems.
“A parallel application only runs as fast as the slowest process,” Brightwell explains. “Think of processes as individual workers at their desks and OS noise as the boss stopping by and interrupting one of the workers. Our study showed that it’s better for the boss to pop his head in several times a day rather than sit down in each office once a day.”
Most software architects, however, prefer to see the boss as infrequently as possible.
“Unfortunately, a number of system software designers … are aggregating periodic work,” the team says in its study, named a “best paper” at SC08, the country’s leading supercomputing conference (see sidebar). “Our results suggest that while this approach may reduce the noise … it is also likely to degrade application performance.”
