Bellosa, Frank
:
Memory Access - The Third Dimension of Scheduling.
Erlangen:
FAU.
1997
TR-I4-97-01.- Interner Bericht.
8 Seiten.
Abstract:
Up to now, two internal events influence scheduling decisions of contemporary
operating systems: timer events and I/O-related interrupts. Timing information
supports preemption and priority adjustment. Knowledge about issued or completed
I/O operations helps to wake-up sleeping processes and to boost their priority.
Preferring deblocked processes at the end of I/O operations improves the interactive
performance and saves buffer space because available data is consumed short after
its availability.
With the upcoming of processors clocked with hundreds of megahertz, the processor
speed exceeds the speed of affordable memory by factors. If it is accepted to
influence execution priorities by slow I/O events, why should scheduling neglect
events related to other slow devices like main memory and memory data paths?
Our novel approach to scheduling is based on knowledge derived from counters in
the memory subsystem. We demonstrate that the usage of information related to
cache- and main-memory access opens new dimensions in real-time and time-slice
scheduling of shared-memory architectures. Advanced cache-affinity scheduling,
memory-bandwidth guarantees for real-time jobs, and new processor assignment
strategies are three basic concepts of a new scheduling philosophy focusing more
on memory access than on CPU cycles as the performance determinant factor.
