.\" Copyright (c) 2017 George V. Neville-Neil <gnn@FreeBSD.org>
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.Dd August 20, 2019
.Dt DTRACE_LOCKSTAT 4
.Os
.Sh NAME
.Nm dtrace_lockstat
.Nd a DTrace provider for tracing CPU scheduling events
.Sh SYNOPSIS
.Fn lockstat:::adaptive-acquire "struct mtx *"
.Fn lockstat:::adaptive-release "struct mtx *"
.Fn lockstat:::adaptive-spin "struct mtx *" "uint64_t"
.Fn lockstat:::adaptive-block "struct mtx *" "uint64_t"
.Fn lockstat:::spin-acquire "struct mtx *"
.Fn lockstat:::spin-release "struct mtx *"
.Fn lockstat:::spin-spin "struct mtx *" "uint64_t"
.Fn lockstat:::rw-acquire "struct rwlock *" "int"
.Fn lockstat:::rw-release "struct rwlock *" "int"
.Fn lockstat:::rw-block "struct rwlock *" "uint64_t" "int" "int" "int"
.Fn lockstat:::rw-spin "struct rwlock *" "uint64_t"
.Fn lockstat:::rw-upgrade "struct rwlock *"
.Fn lockstat:::rw-downgrade "struct rwlock *"
.Fn lockstat:::sx-acquire "struct sx *" "int"
.Fn lockstat:::sx-release "struct sx *" "int"
.Fn lockstat:::sx-block "struct sx *" "uint64_t" "int" "int" "int"
.Fn lockstat:::sx-spin "struct sx *" "uint64_t"
.Fn lockstat:::sx-upgrade "struct sx *"
.Fn lockstat:::sx-downgrade "struct sx *"
.Fn lockstat:::lockmgr-acquire "struct lock *" "int"
.Fn lockstat:::lockmgr-release "struct lock *" "int"
.Fn lockstat:::lockmgr-disown "struct lock *" "int"
.Fn lockstat:::lockmgr-block "struct lock *" "uint64_t" "int" "int" "int"
.Fn lockstat:::lockmgr-upgrade "struct lock *"
.Fn lockstat:::lockmgr-downgrade "struct lock *"
.Fn lockstat:::thread-spin "struct mtx *" "uint64"
.Sh DESCRIPTION
The DTrace
.Nm lockstat
provider allows the tracing of events related to locking on
.Fx .
.Pp
The
.Nm
provider contains DTrace probes for inspecting kernel lock
state transitions.
Probes exist for the
.Xr lockmgr 9 ,
.Xr mutex 9 ,
.Xr rwlock 9 ,
and
.Xr sx 9
lock types.
The
.Xr lockstat 1
utility can be used to collect and display data collected from the
.Nm
provider.
Each type of lock has
.Fn acquire
and
.Fn release
probes which expose the lock structure being operated upon,
as well as probes which fire when a thread contends with other threads
for ownership of a lock.
.Pp
The
.Fn lockstat:::adaptive-acquire
and
.Fn lockstat:::adaptive-release
probes fire when an
.Dv MTX_DEF
.Xr mutex 9
is acquired and released, respectively.
The only argument is a pointer to the lock structure which describes
the lock being acquired or released.
.Pp
The
.Fn lockstat:::adaptive-spin
probe fires when a thread spins while waiting for a
.Dv MTX_DEF
.Xr mutex 9
to be released by another thread.
The first argument is a pointer to the lock structure that describes
the lock and the second argument is the amount of time,
in nanoseconds, that the mutex spent spinning.
The
.Fn lockstat:::adaptive-block
probe fires when a thread takes itself off the CPU while trying to acquire an
.Dv MTX_DEF
.Xr mutex 9
that is owned by another thread.
The first argument is a pointer to the lock structure that describes
the lock and the second argument is the length of time,
in nanoseconds, that the waiting thread was blocked.
The
.Fn lockstat:::adaptive-block
and
.Fn lockstat:::adaptive-spin
probes fire only after the lock has been successfully acquired,
and in particular, after the
.Fn lockstat:::adaptive-acquire
probe fires.
.Pp
The
.Fn lockstat:::spin-acquire
and
.Fn lockstat:::spin-release
probes fire when a
.Dv MTX_SPIN
.Xr mutex 9
is acquired or released, respectively.
The only argument is a pointer to the lock structure which describes
the lock being acquired or released.
.Pp
The
.Fn lockstat:::spin-spin
probe fires when a thread spins while waiting for a
.Dv MTX_SPIN
.Xr mutex 9
to be released by another thread.
The first argument is a pointer to the lock structure that describes
the lock and the second argument is the length of the time
spent spinning, in nanoseconds.
The
.Fn lockstat:::spin-spin
probe fires only after the lock has been successfully acquired,
and in particular, after the
.Fn lockstat:::spin-acquire
probe fires.
.Pp
The
.Fn lockstat:::rw-acquire
and
.Fn lockstat:::rw-release
probes fire when a
.Xr rwlock 9
is acquired or released, respectively.
The first argument is a pointer to the structure which describes
the lock being acquired.
The second argument is
.Dv 0
if the lock is being acquired or released as a writer, and
.Dv 1
if it is being acquired or released as a reader.
The
.Fn lockstat:::sx-acquire
and
.Fn lockstat:::sx-release ,
and
.Fn lockstat:::lockmgr-acquire
and
.Fn lockstat:::lockmgr-release
probes fire upon the corresponding events for
.Xr sx 9
and
.Xr lockmgr 9
locks, respectively.
The
.Fn lockstat:::lockmgr-disown
probe fires when a
.Xr lockmgr 9
exclusive lock is disowned.
In this state, the lock remains exclusively held, but may be
released by a different thread.
The
.Fn lockstat:::lockmgr-release
probe does not fire when releasing a disowned lock.
The first argument is a pointer to the structure which describes
the lock being disowned.
The second argument is
.Dv 0 ,
for compatibility with
.Fn lockstat:::lockmgr-release .
.Pp
The
.Fn lockstat:::rw-block ,
.Fn lockstat:::sx-block ,
and
.Fn lockstat:::lockmgr-block
probes fire when a thread removes itself from the CPU while
waiting to acquire a lock of the corresponding type.
The
.Fn lockstat:::rw-spin
and
.Fn lockstat:::sx-spin
probes fire when a thread spins while waiting to acquire a lock
of the corresponding type.
All probes take the same set of arguments.
The first argument is a pointer to the lock structure that describes
the lock.
The second argument is the length of time, in nanoseconds,
that the waiting thread was off the CPU or spinning for the lock.
The third argument is
.Dv 0
if the thread is attempting to acquire the lock as a writer, and
.Dv 1
if the thread is attempting to acquire the lock as a reader.
The fourth argument is
.Dv 0
if the thread is waiting for a reader to release the lock, and
.Dv 1
if the thread is waiting for a writer to release the lock.
The fifth argument is the number of readers that held the lock when
the thread first attempted to acquire the lock.
This argument will be
.Dv 0
if the fourth argument is
.Dv 1 .
.Pp
The
.Fn lockstat:::lockmgr-upgrade ,
.Fn lockstat:::rw-upgrade ,
and
.Fn lockstat:::sx-upgrade
probes fire when a thread successfully upgrades a held
.Xr lockmgr 9 ,
.Xr rwlock 9 ,
or
.Xr sx 9
shared/reader lock to an exclusive/writer lock.
The only argument is a pointer to the structure which describes
the lock being acquired.
The
.Fn lockstat:::lockmgr-downgrade ,
.Fn lockstat:::rw-downgrade ,
and
.Fn lockstat:::sx-downgrade
probes fire when a thread downgrades a held
.Xr lockmgr 9 ,
.Xr rwlock 9 ,
or
.Xr sx 9
exclusive/writer lock to a shared/reader lock.
.Pp
The
.Fn lockstat:::thread-spin
probe fires when a thread spins on a thread lock, which is a specialized
.Dv MTX_SPIN
.Xr mutex 9 .
The first argument is a pointer to the structure that describes
the lock and the second argument is the length of time,
in nanoseconds, that the thread was spinning.
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr lockstat 1 ,
.Xr locking 9 ,
.Xr mutex 9 ,
.Xr rwlock 9 ,
.Xr SDT 9 ,
.Xr sx 9
.Sh HISTORY
The
.Nm
provider first appeared in Solaris.
The
.Fx
implementation of the
.Nm
provider first appeared in
.Fx 9 .
.Sh AUTHORS
This manual page was written by
.An George V. Neville-Neil Aq Mt gnn@FreeBSD.org
and
.An -nosplit
.An Mark Johnston Aq Mt markj@FreeBSD.org .
.Sh BUGS
Probes for
.Xr rmlock 9
locks have not yet been added.