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sched_4bsd — 4.4BSD scheduler
The sched_4bsd scheduler is the traditional system scheduler, providing
both high throughput and solid interactive response in the presence of
The following sysctls are relevant to the operation of sched_4bsd:
This read-only sysctl reports the name of the active scheduler.
This read-write sysctl reports or sets the length of the quantum
(in micro-seconds) granted to a thread.
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.
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.
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.