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tracing: Add per-element variable support to tracing_map
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In order to allow information to be passed between trace events, add
support for per-element variables to tracing_map.  This provides a
means for histograms to associate a value or values with an entry when
it's saved or updated, and retrieved by a subsequent event occurrences.

Variables can be set using tracing_map_set_var() and read using
tracing_map_read_var().  tracing_map_var_set() returns true or false
depending on whether or not the variable has been set or not, which is
important for event-matching applications.

tracing_map_read_var_once() reads the variable and resets it to the
'unset' state, implementing read-once variables, which are also
important for event-matching uses.

Link: http://lkml.kernel.org/r/7fa001108252556f0c6dd9d63145eabfe3370d1a.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Tom Zanussi authored and Steven Rostedt (VMware) committed Mar 10, 2018
1 parent ad42feb commit 2734b62
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Showing 2 changed files with 119 additions and 0 deletions.
108 changes: 108 additions & 0 deletions kernel/trace/tracing_map.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,73 @@ u64 tracing_map_read_sum(struct tracing_map_elt *elt, unsigned int i)
return (u64)atomic64_read(&elt->fields[i].sum);
}

/**
* tracing_map_set_var - Assign a tracing_map_elt's variable field
* @elt: The tracing_map_elt
* @i: The index of the given variable associated with the tracing_map_elt
* @n: The value to assign
*
* Assign n to variable i associated with the specified tracing_map_elt
* instance. The index i is the index returned by the call to
* tracing_map_add_var() when the tracing map was set up.
*/
void tracing_map_set_var(struct tracing_map_elt *elt, unsigned int i, u64 n)
{
atomic64_set(&elt->vars[i], n);
elt->var_set[i] = true;
}

/**
* tracing_map_var_set - Return whether or not a variable has been set
* @elt: The tracing_map_elt
* @i: The index of the given variable associated with the tracing_map_elt
*
* Return true if the variable has been set, false otherwise. The
* index i is the index returned by the call to tracing_map_add_var()
* when the tracing map was set up.
*/
bool tracing_map_var_set(struct tracing_map_elt *elt, unsigned int i)
{
return elt->var_set[i];
}

/**
* tracing_map_read_var - Return the value of a tracing_map_elt's variable field
* @elt: The tracing_map_elt
* @i: The index of the given variable associated with the tracing_map_elt
*
* Retrieve the value of the variable i associated with the specified
* tracing_map_elt instance. The index i is the index returned by the
* call to tracing_map_add_var() when the tracing map was set
* up.
*
* Return: The variable value associated with field i for elt.
*/
u64 tracing_map_read_var(struct tracing_map_elt *elt, unsigned int i)
{
return (u64)atomic64_read(&elt->vars[i]);
}

/**
* tracing_map_read_var_once - Return and reset a tracing_map_elt's variable field
* @elt: The tracing_map_elt
* @i: The index of the given variable associated with the tracing_map_elt
*
* Retrieve the value of the variable i associated with the specified
* tracing_map_elt instance, and reset the variable to the 'not set'
* state. The index i is the index returned by the call to
* tracing_map_add_var() when the tracing map was set up. The reset
* essentially makes the variable a read-once variable if it's only
* accessed using this function.
*
* Return: The variable value associated with field i for elt.
*/
u64 tracing_map_read_var_once(struct tracing_map_elt *elt, unsigned int i)
{
elt->var_set[i] = false;
return (u64)atomic64_read(&elt->vars[i]);
}

int tracing_map_cmp_string(void *val_a, void *val_b)
{
char *a = val_a;
Expand Down Expand Up @@ -170,6 +237,28 @@ int tracing_map_add_sum_field(struct tracing_map *map)
return tracing_map_add_field(map, tracing_map_cmp_atomic64);
}

/**
* tracing_map_add_var - Add a field describing a tracing_map var
* @map: The tracing_map
*
* Add a var to the map and return the index identifying it in the map
* and associated tracing_map_elts. This is the index used for
* instance to update a var for a particular tracing_map_elt using
* tracing_map_update_var() or reading it via tracing_map_read_var().
*
* Return: The index identifying the var in the map and associated
* tracing_map_elts, or -EINVAL on error.
*/
int tracing_map_add_var(struct tracing_map *map)
{
int ret = -EINVAL;

if (map->n_vars < TRACING_MAP_VARS_MAX)
ret = map->n_vars++;

return ret;
}

/**
* tracing_map_add_key_field - Add a field describing a tracing_map key
* @map: The tracing_map
Expand Down Expand Up @@ -280,6 +369,11 @@ static void tracing_map_elt_clear(struct tracing_map_elt *elt)
if (elt->fields[i].cmp_fn == tracing_map_cmp_atomic64)
atomic64_set(&elt->fields[i].sum, 0);

for (i = 0; i < elt->map->n_vars; i++) {
atomic64_set(&elt->vars[i], 0);
elt->var_set[i] = false;
}

if (elt->map->ops && elt->map->ops->elt_clear)
elt->map->ops->elt_clear(elt);
}
Expand All @@ -306,6 +400,8 @@ static void tracing_map_elt_free(struct tracing_map_elt *elt)
if (elt->map->ops && elt->map->ops->elt_free)
elt->map->ops->elt_free(elt);
kfree(elt->fields);
kfree(elt->vars);
kfree(elt->var_set);
kfree(elt->key);
kfree(elt);
}
Expand Down Expand Up @@ -333,6 +429,18 @@ static struct tracing_map_elt *tracing_map_elt_alloc(struct tracing_map *map)
goto free;
}

elt->vars = kcalloc(map->n_vars, sizeof(*elt->vars), GFP_KERNEL);
if (!elt->vars) {
err = -ENOMEM;
goto free;
}

elt->var_set = kcalloc(map->n_vars, sizeof(*elt->var_set), GFP_KERNEL);
if (!elt->var_set) {
err = -ENOMEM;
goto free;
}

tracing_map_elt_init_fields(elt);

if (map->ops && map->ops->elt_alloc) {
Expand Down
11 changes: 11 additions & 0 deletions kernel/trace/tracing_map.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
#define TRACING_MAP_VALS_MAX 3
#define TRACING_MAP_FIELDS_MAX (TRACING_MAP_KEYS_MAX + \
TRACING_MAP_VALS_MAX)
#define TRACING_MAP_VARS_MAX 16
#define TRACING_MAP_SORT_KEYS_MAX 2

typedef int (*tracing_map_cmp_fn_t) (void *val_a, void *val_b);
Expand Down Expand Up @@ -137,6 +138,8 @@ struct tracing_map_field {
struct tracing_map_elt {
struct tracing_map *map;
struct tracing_map_field *fields;
atomic64_t *vars;
bool *var_set;
void *key;
void *private_data;
};
Expand Down Expand Up @@ -192,6 +195,7 @@ struct tracing_map {
int key_idx[TRACING_MAP_KEYS_MAX];
unsigned int n_keys;
struct tracing_map_sort_key sort_key;
unsigned int n_vars;
atomic64_t hits;
atomic64_t drops;
};
Expand Down Expand Up @@ -241,6 +245,7 @@ tracing_map_create(unsigned int map_bits,
extern int tracing_map_init(struct tracing_map *map);

extern int tracing_map_add_sum_field(struct tracing_map *map);
extern int tracing_map_add_var(struct tracing_map *map);
extern int tracing_map_add_key_field(struct tracing_map *map,
unsigned int offset,
tracing_map_cmp_fn_t cmp_fn);
Expand All @@ -260,7 +265,13 @@ extern int tracing_map_cmp_none(void *val_a, void *val_b);

extern void tracing_map_update_sum(struct tracing_map_elt *elt,
unsigned int i, u64 n);
extern void tracing_map_set_var(struct tracing_map_elt *elt,
unsigned int i, u64 n);
extern bool tracing_map_var_set(struct tracing_map_elt *elt, unsigned int i);
extern u64 tracing_map_read_sum(struct tracing_map_elt *elt, unsigned int i);
extern u64 tracing_map_read_var(struct tracing_map_elt *elt, unsigned int i);
extern u64 tracing_map_read_var_once(struct tracing_map_elt *elt, unsigned int i);

extern void tracing_map_set_field_descr(struct tracing_map *map,
unsigned int i,
unsigned int key_offset,
Expand Down

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