PCU(9) FreeBSD Kernel Developer's Manual PCU(9)
NAME
pcu - per-CPU unit (PCU)
SYNOPSIS
#include <sys/pcu.h>
void
pcu_load(const pcu_ops_t *pcu);
void
pcu_save(const pcu_ops_t *pcu, lwp_t *l);
void
pcu_save_all(lwp_t *l);
void
pcu_discard(const pcu_ops_t *pcu, lwp_t *l, bool valid);
void
pcu_discard_all(lwp_t *l);
bool
pcu_valid_p(const pcu_ops_t *pcu);
DESCRIPTION
Per CPU Unit (PCU) is an interface to manage synchronization of any per-
CPU context (unit) tied to an LWP context. Typical use of PCU is for
"lazy-switch" synchronization of the FPU state. Each PCU has its
operations defined by a pcu_ops_t structure. Members of pcu_ops_t are
u_int pcu_id;
void (*pcu_state_save)(lwp_t *l);
void (*pcu_state_load)(lwp_t *l, u_int flags);
void (*pcu_state_release)(lwp_t *l);
pcu_state_save()
Indicate to MD code that the PCU state on the current CPU should
be saved into the given LWP's MD storage.
pcu_state_load()
Load PCU state from the given LWP's MD storage to the current
CPU. The flags argument is a combination of one or more of the
following:
PCU_VALID Indicate that the PCU state is considered valid and
need not be initialized. This is the case if the
PCU state was already used (and thus loaded) by the
LWP and has not been discarded since.
PCU_REENABLE Indicate that a fault reoccurred while the PCU
state is loaded, therefore PCU should be re-
enabled. This happens if LWP is context switched
to another CPU and then switched back to the
original CPU while the state on that CPU has not
been changed by other LWPs. It may also happen due
to instruction "bouncing" on some architectures.
pcu_state_release()
Indicate to MD code that the PCU ownership by the LWP was
released, therefore the next use of PCU on the LWP shall be
detected and pcu_load() be called to reacquire the ownership.
For example, this would normally be the changing of a bit for a
CPU to trap on the execution of one of the PCU's instructions.
FUNCTIONS
pcu_load() Load or initialize the PCU state of the current LWP on
the current CPU.
pcu_save() Save the specified PCU state to the given LWP.
pcu_discard() Discard the specified PCU state of the current LWP. The
PCU state will be considered invalid, unless the "valid"
parameter is set to true.
pcu_valid_p() Return true if PCU state is considered valid.
Generally, it always becomes "valid" when pcu_load() is
called by the LWP. Otherwise, return false.
pcu_discard_all()
Discard all PCU states of the given LWP; generally used
by exec and exit.
pcu_save_all() Save all PCU states of the given LWP; generally used
during new LWP creation so that the PCU state of the
parent could be copied.
CODE REFERENCES
pcu is implemented within the file sys/kern/subr_pcu.c.
HISTORY
PCU first appeared in NetBSD 6.0.
AUTHORS
Mindaugas Rasiukevicius <
[email protected]>
FreeBSD 14.1-RELEASE-p8 May 16, 2017 FreeBSD 14.1-RELEASE-p8