bionic (4) dtrace_sched.4freebsd.gz
NAME
dtrace_sched — a DTrace provider for tracing CPU scheduling events
SYNOPSIS
sched:::change-pri(struct thread *, struct proc *, uint8_t);
sched:::dequeue(struct thread *, struct proc *, void *);
sched:::enqueue(struct thread *, struct proc *, void *, int);
sched:::lend-pri(struct thread *, struct proc *, uint8_t, struct thread *);
sched:::load-change(int, int);
sched:::off-cpu(struct thread *, struct proc *);
sched:::on-cpu();
sched:::preempt();
sched:::remain-cpu();
sched:::surrender(struct thread *, struct proc *);
sched:::sleep();
sched:::tick(struct thread *, struct proc *);
sched:::wakeup(struct thread *, struct proc *);
DESCRIPTION
The DTrace sched provider allows the tracing of events related to CPU scheduling in the 4BSD and ULE
schedulers.
The sched:::change-pri() probe fires when a thread's active scheduling priority is about to be updated.
The first two arguments are the thread whose priority is about to be changed, and the corresponding
process. The third argument is the new absolute priority for the thread, while the current value is given
by args[0]->td_priority. The sched:::lend-pri() probe fires when the currently-running thread elevates the
priority of another thread via priority lending. The first two arguments are the thread whose priority is
about to be changed, and the corresponding process. The third argument is the new absolute priority for
the thread. The fourth argument is the currently-running thread.
The sched:::dequeue() probe fires immediately before a runnable thread is removed from a scheduler run
queue. This may occur when the thread is about to begin execution on a CPU, or because the thread is being
migrated to a different run queue. The latter event may occur in several circumstances: the scheduler may
be attempting to rebalance load between multiple CPUs, the thread's scheduling priority may have changed,
or the thread's CPU affinity settings may have changed. The first two arguments to sched:::dequeue() are
the thread and corresponding process. The third argument is currently always NULL. The sched:::enqueue()
probe fires when a runnable thread is about to be added to a scheduler run queue. Its first two arguments
are the thread and corresponding process. The third argument is currently always NULL. The fourth
argument is a boolean value that is non-zero if the thread is enqueued at the beginning of its run queue
slot, and zero if the thread is instead enqueued at the end.
The sched:::load-change() probe fires after the load of a thread queue is adjusted. The first argument is
the cpuid for the CPU associated with the thread queue, and the second argument is the adjusted load of the
thread queue, i.e., the number of elements in the queue.
The sched:::off-cpu() probe is triggered by the scheduler suspending execution of the currently-running
thread, and the sched:::on-cpu() probe fires when the current thread has been selected to run on a CPU and
is about to begin or resume execution. The arguments to sched:::off-cpu() are the thread and corresponding
process selected to run following the currently-running thread. If these two threads are the same, the
sched:::remain-cpu() probe will fire instead.
The sched:::surrender() probe fires when the scheduler is called upon to make a scheduling decision by a
thread running on a different CPU, via an interprocessor interrupt. The arguments to this probe are the
interrupted thread and its corresponding process. This probe currently always fires in the context of the
interrupted thread.
The sched:::preempt() probe will fire immediately before the currently-running thread is preempted. When
this occurs, the scheduler will select a new thread to run, and one of the sched:::off-cpu() or
sched:::remain-cpu() probes will subsequently fire, depending on whether or not the scheduler selects the
preempted thread.
The sched:::sleep() probe fires immediately before the currently-running thread is about to suspend
execution and begin waiting for a condition to be met. The sched:::wakeup() probe fires when a thread is
set up to resume execution after having gone to sleep. Its arguments are the thread being awoken, and the
corresponding process.
The sched:::tick() fires before each scheduler clock tick. Its arguments are the currently-running thread
and its corresponding process.
ARGUMENTS
The sched provider probes use the kernel types struct proc and struct thread to represent processes and
threads, respectively. These structures have many fields and are defined in sys/proc.h. In a probe body,
the currently-running thread can always be obtained with the curthread global variable, which has type
struct thread *. For example, when a running thread is about to sleep, the sched:::sleep() probe fires in
the context of that thread, which can be accessed using curthread. The curcpu global variable contains the
cpuid of the CPU on which the currently-running thread is executing.
EXAMPLES
The following script gives a breakdown of CPU utilization by process name:
sched:::on-cpu
{
self->ts = timestamp;
}
sched:::off-cpu
/self->ts != 0/
{
@[execname] = sum((timestamp - self->ts) / 1000);
self->ts = 0;
}
Here, DTrace stores a timestamp each time a thread is scheduled to run, and computes the time elapsed in
microseconds when it is descheduled. The results are summed by process name.
COMPATIBILITY
This provider is not compatible with the sched provider found in Solaris. In particular, the probe
argument types are native FreeBSD types, and the sched:::cpucaps-sleep(), sched:::cpucaps-wakeup(),
sched:::schedctl-nopreempt(), sched:::schedctl-preempt(), and sched:::schedctl-yield() probes are not
available in FreeBSD.
The sched:::lend-pri() and sched:::load-change() probes are specific to FreeBSD.
SEE ALSO
dtrace(1), sched_4bsd(4), sched_ule(4), SDT(9), sleepqueue(9)
HISTORY
The sched provider first appeared in FreeBSD 8.4 and 9.1.
AUTHORS
This manual page was written by Mark Johnston <markj@FreeBSD.org>.