pcu(9)
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PCU(9) NetBSD 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 opera-
tions 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. Gener-
ally, 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 <rmind@NetBSD.org>
NetBSD 10.99 May 16, 2017 NetBSD 10.99
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