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
<
rmind@NetBSD.org>