sched_4bsd —
4.4BSD scheduler
options SCHED_4BSD
The
sched_4bsd scheduler is the traditional system
scheduler, providing both high throughput and solid interactive response in
the presence of load.
The following sysctls are relevant to the operation of
sched_4bsd:
- kern.sched.name
- This read-only sysctl reports the name of the active
scheduler.
- kern.sched.quantum
- This read-write sysctl reports or sets the length of the
quantum (in micro-seconds) granted to a thread.
- kern.sched.ipiwakeup.enabled
- This read-write sysctl sets whether or not the scheduler
will generate an inter-processor interrupt (IPI) to an idle CPU when a
thread is woken up. Otherwise, idle CPUs will wait until the next clock
tick before looking for new work.
- kern.sched.preemption
- This read-only sysctl reports whether or not the kernel is
configured to support preemption, which reduces the latency to run lower
priority threads on wakeup.
Some sysctls will be available only on systems supporting SMP.
sched_ule(4),
sysctl(8)
The
sched_4bsd scheduler has been present, in
various forms, since the inception of
BSD.
While a highly robust and time-tested scheduler,
sched_4bsd lacks specific knowledge of how to
schedule advantageously in non-symmetric processor configurations, such as
hyper-threading.