evcnt, evcnt_attach_dynamic, evcnt_attach_static, evcnt_detach - generic
event counter framework
#include <sys/device.h>
void
evcnt_attach_dynamic(struct evcnt *ev, int type,
const struct evcnt *parent, const char *group, const char *name);
void
evcnt_attach_static(struct evcnt *ev);
void
evcnt_detach(struct evcnt *ev);
The NetBSD generic event counter framework is designed to provide a flexible
and hierarchical event counting facility, which is useful for tracking
system events (including device interrupts).
The fundamental component of this framework is the evcnt structure. Its
user-accessible fields are:
struct evcnt {
u_int64_t ev_count; /* how many have occurred */
TAILQ_ENTRY(evcnt) ev_list; /* entry on list of all counters */
unsigned char ev_type; /* counter type; see below */
unsigned char ev_grouplen; /* 'group' len, excluding NUL */
unsigned char ev_namelen; /* 'name' len, excluding NUL */
const struct evcnt *ev_parent; /* parent, for hierarchical ctrs */
const char *ev_group; /* name of group */
const char *ev_name; /* name of specific event */
};
The system maintains a global linked list of all active event counters.
This list, called allevents, may grow or shrink over time as event counters
are dynamically added to and removed from the system.
Each event counter is marked (in the ev_type field) with the type of
event being counted. The following types are currently defined:
EVCNT_TYPE_MISC Miscellaneous; doesn't fit into one of the other
types.
EVCNT_TYPE_INTR Interrupt counter, reported by vmstat -i.
Each event counter also has a group name (ev_group) and an event name
(ev_name) which are used to identify the counter. The group name may be
shared by a set of counters. For example, device interrupt counters
would use the name of the device whose interrupts are being counted as
the group name. The counter name is meant to distinguish the counter
from others in its group (and need not be unique across groups). Both
names should be understandable by users, since they are printed by commands
like vmstat(1). The constant EVCNT_STRING_MAX is defined to be the
maximum group or event name length in bytes (including the trailing NUL).
In the current implementation it is 256.
To support hierarchical tracking of events, each event counter can name a
``parent'' event counter. For instance, interrupt dispatch code could
have an event counter per interrupt line, and devices could each have
counters for the number of interrupts that they were responsible for
causing. In that case, the counter for a device on a given interrupt
line would have the line's counter as its parent. The value NULL is be
used to indicate that a counter has no parent. A counter's parent must
be attached before the counter is attached, and detached after the
counter is detached.
The EVCNT_INITIALIZER() macro can be used to provide a static initializer
for an event counter structure. It is be invoked as
EVCNT_INITIALIZER(type, parent, group, name), and its arguments will be
placed into the corresponding fields of the event counter structure it is
initializing. The group and name arguments must be constant strings.
The following is a brief description of each function in the framework:
void evcnt_attach_dynamic(struct evcnt *ev, int type, const struct evcnt
*parent, const char *group, const char *name)
Attach the event counter structure pointed to by ev to the system
event list. The event counter is cleared and its fields initialized
using the arguments to the function call. The contents of
the remaining elements in the structure (e.g., the name lengths)
are calculated, and the counter is added to the system event
list.
The strings specified as the group and counter names must persist
(with the same value) throughout the life of the event counter;
they are referenced by, not copied into, the counter.
void evcnt_attach_static(struct evcnt *ev)
Attach the statically-initialized event counter structure pointed
to by ev to the system event list. The event counter is assumed
to be statically initialized using the EVCNT_INITIALIZER() macro.
This function simply calculates structure elements' values as
appropriate (e.g., the string lengths), and adds the counter to
the system event list.
void evcnt_detach(struct evcnt *ev)
Detach the event counter structure pointed to by ev from the system
event list.
Note that no method is provided to increment the value of an event
counter. Code incrementing an event counter should do so by directly
accessing its ev_count field in a manner that is known to be safe. For
instance, additions to a device's event counters in the interrupt handler
for that device will often be safe without additional protection (because
interrupt handler entries for a given device have to be serialized).
However, for other uses of event counters, additional locking or use of
machine-dependent atomic operation may be appropriate. (The overhead of
using a mechanism that is guaranteed to be safe to increment every
counter, regardless of actual need for such a mechanism where the counter
is being incremented, would be too great. On some systems, it might
involve a global lock and several function calls.)
This section includes a description on basic use of the framework and
example usage of its functions.
Device drivers can use the evcnt_attach_dynamic() and evcnt_detach()
functions to manage device-specific event counters. Statically configured
system modules can use evcnt_attach_static() to configure global
event counters. Similarly, loadable modules can use
evcnt_attach_static() to configure their global event counters,
evcnt_attach_dynamic() to attach device-specific event counters, and
evcnt_detach() to detach all counters when being unloaded.
Device drivers that wish to use the generic event counter framework
should place event counter structures in their ``softc'' structures. For
example, to keep track of the number of interrupts for a given device
(broken down further into ``device readable'' and ``device writable''
interrupts) a device driver might use:
struct foo_softc {
struct device sc_dev; /* generic device information */
[ . . . ]
struct evcnt sc_ev_intr; /* interrupt count */
struct evcnt sc_ev_intr_rd; /* 'readable' interrupt count */
struct evcnt sc_ev_intr_wr; /* 'writable' interrupt count */
[ . . . ]
};
In the device attach function, those counters would be registered with
the system using the evcnt_attach_dynamic() function, using code like:
void
fooattach(parent, self, aux)
struct device *parent, *self;
void *aux;
{
struct foo_softc *sc = (struct foo_softc *)self;
[ . . . ]
/* Initialize and attach event counters. */
evcnt_attach_dynamic(sc->sc_ev, EVCNT_TYPE_INTR,
NULL, sc->sc_dev.dv_xname, "intr");
evcnt_attach_dynamic(sc->sc_ev_rd, EVCNT_TYPE_INTR,
sc->sc_ev, sc->sc_dev.dv_xname, "intr rd");
evcnt_attach_dynamic(sc->sc_ev_wr, EVCNT_TYPE_INTR,
sc->sc_ev, sc->sc_dev.dv_xname, "intr wr");
[ . . . ]
}
If the device can be detached from the system, its detach function should
invoke evcnt_detach() on each attached counter (making sure to detach any
``parent'' counters only after detaching all children).
Code like the following might be used to initialize a static event
counter (in this example, one used to track CPU alignment traps):
struct evcnt aligntrap_ev = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
NULL, "cpu", "aligntrap")
To attach this event counter, code like the following could be used:
evcnt_attach_static(aligntrap_ev);
This section describes places within the NetBSD source tree where actual
code implementing or utilizing the event counter framework can be found.
All pathnames are relative to /usr/src.
The event counter framework itself is implemented within the file
sys/kern/subr_autoconf.c. Data structures and function prototypes for
the framework are located in sys/sys/device.h.
Event counters are used throughout the system.
The vmstat(1) source file usr.bin/vmstat/vmstat.c shows an example of how
to access event counters from user programs.
vmstat(1)
A set of interrupt counter interfaces with similar names to the interfaces
in the NetBSD generic event counter framework appeared as part of
the new autoconfiguration system in 4.4BSD. Those interfaces were never
widely adopted in NetBSD because of limitations in their applicability.
(Their use was limited to non-hierarchical, dynamically attached device
interrupt counters.) The NetBSD generic event counter framework first
appeared in NetBSD 1.5.
The NetBSD generic event counter framework was designed and implemented
by Chris Demetriou <[email protected]>.
BSD June 1, 2000 BSD
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