Interaction Abstract
The Interaction of Parallel and Sequential Workloads on a Network of
Workstations
This paper examines the plausibility of using a network of workstations
(NOW) for a mixture of parallel and sequential jobs. Through
simulations, our study examines issues that arise when combining these
two workloads on a single platform. Starting from a dedicated NOW just
for parallel programs, we incrementally relax uniprogramming
restrictions until we have a multi-programmed, multi-user NOW for both
interactive sequential users and parallel programs. We show that a
number of issues associated with the distributed NOW environment (e.g.,
daemon activity, coscheduling skew) can have a small but noticeable
effect on parallel program performance. We also find that efficient
migration to idle workstations is necessary to maintain acceptable
parallel application performance. Furthermore, we present a methodology
for deriving an optimal delay time for recruiting idle machines for use
by parallel programs; this {\em recruitment threshold} was just 3
minutes for the research cluster we measured. Finally, we quantify the
effects of the additional parallel load upon interactive users by
keeping track of the potential number of {\em user delays} in our
simulations. When we limit the maximum number of delays per user, we
can still maintain acceptable parallel program performance. In summary,
we find that for our workloads a 2:1 rule applies: a NOW cluster of
approximately 60 machines can sustain a 32-node parallel workload in
addition to the sequential load placed upon it by interactive users.