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tracing: Add linear buckets to histogram logic
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There's been several times I wished the histogram logic had a "grouping"
feature for the buckets. Currently, each bucket has a size of one. That
is, if you trace the amount of requested allocations, each allocation is
its own bucket, even if you are interested in what allocates 100 bytes or
less, 100 to 200, 200 to 300, etc.

Also, without grouping, it fills up the allocated histogram buckets
quickly. If you are tracking latency, and don't care if something is 200
microseconds off, or 201 microseconds off, but want to track them by say
10 microseconds each. This can not currently be done.

There is a log2 but that grouping get's too big too fast for a lot of
cases.

Introduce a "buckets=SIZE" command to each field where it will record in a
rounded number. For example:

 ># echo 'hist:keys=bytes_req.buckets=100:sort=bytes_req' > events/kmem/kmalloc/trigger
 ># cat events/kmem/kmalloc/hist
 # event histogram
 #
 # trigger info:
 hist:keys=bytes_req.buckets=100:vals=hitcount:sort=bytes_req.buckets=100:size=2048
 [active]
 #

 { bytes_req: ~ 0-99 } hitcount:       3149
 { bytes_req: ~ 100-199 } hitcount:       1468
 { bytes_req: ~ 200-299 } hitcount:         39
 { bytes_req: ~ 300-399 } hitcount:        306
 { bytes_req: ~ 400-499 } hitcount:        364
 { bytes_req: ~ 500-599 } hitcount:         32
 { bytes_req: ~ 600-699 } hitcount:         69
 { bytes_req: ~ 700-799 } hitcount:         37
 { bytes_req: ~ 1200-1299 } hitcount:         16
 { bytes_req: ~ 1400-1499 } hitcount:         30
 { bytes_req: ~ 2000-2099 } hitcount:          6
 { bytes_req: ~ 4000-4099 } hitcount:       2168
 { bytes_req: ~ 5000-5099 } hitcount:          6

 Totals:
     Hits: 7690
     Entries: 13
     Dropped: 0

Link: https://lkml.kernel.org/r/[email protected]

Acked-by: Namhyung Kim <[email protected]>
Reviewed-by: Tom Zanussi <[email protected]>
Reviewed-by: Masami Hiramatsu <[email protected]>
Tested-by: Daniel Bristot de Oliveira <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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@rostedt
rostedt committed Aug 16, 2021
1 parent 6fe7c74 commit de9a48a
Showing 1 changed file with 58 additions and 7 deletions.
65 changes: 58 additions & 7 deletions kernel/trace/trace_events_hist.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -121,6 +121,7 @@ struct hist_field {
unsigned int size;
unsigned int offset;
unsigned int is_signed;
unsigned long buckets;
const char *type;
struct hist_field *operands[HIST_FIELD_OPERANDS_MAX];
struct hist_trigger_data *hist_data;
Expand Down Expand Up @@ -219,6 +220,27 @@ static u64 hist_field_log2(struct hist_field *hist_field,
return (u64) ilog2(roundup_pow_of_two(val));
}

static u64 hist_field_bucket(struct hist_field *hist_field,
struct tracing_map_elt *elt,
struct trace_buffer *buffer,
struct ring_buffer_event *rbe,
void *event)
{
struct hist_field *operand = hist_field->operands[0];
unsigned long buckets = hist_field->buckets;

u64 val = operand->fn(operand, elt, buffer, rbe, event);

if (WARN_ON_ONCE(!buckets))
return val;

if (val >= LONG_MAX)
val = div64_ul(val, buckets);
else
val = (u64)((unsigned long)val / buckets);
return val * buckets;
}

static u64 hist_field_plus(struct hist_field *hist_field,
struct tracing_map_elt *elt,
struct trace_buffer *buffer,
Expand Down Expand Up @@ -318,6 +340,7 @@ enum hist_field_flags {
HIST_FIELD_FL_VAR_REF = 1 << 14,
HIST_FIELD_FL_CPU = 1 << 15,
HIST_FIELD_FL_ALIAS = 1 << 16,
HIST_FIELD_FL_BUCKET = 1 << 17,
};

struct var_defs {
Expand Down Expand Up @@ -1109,7 +1132,8 @@ static const char *hist_field_name(struct hist_field *field,
if (field->field)
field_name = field->field->name;
else if (field->flags & HIST_FIELD_FL_LOG2 ||
field->flags & HIST_FIELD_FL_ALIAS)
field->flags & HIST_FIELD_FL_ALIAS ||
field->flags & HIST_FIELD_FL_BUCKET)
field_name = hist_field_name(field->operands[0], ++level);
else if (field->flags & HIST_FIELD_FL_CPU)
field_name = "common_cpu";
Expand Down Expand Up @@ -1470,6 +1494,8 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
flags_str = "syscall";
else if (hist_field->flags & HIST_FIELD_FL_LOG2)
flags_str = "log2";
else if (hist_field->flags & HIST_FIELD_FL_BUCKET)
flags_str = "buckets";
else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP_USECS)
flags_str = "usecs";

Expand Down Expand Up @@ -1658,9 +1684,10 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
goto out;
}

if (flags & HIST_FIELD_FL_LOG2) {
unsigned long fl = flags & ~HIST_FIELD_FL_LOG2;
hist_field->fn = hist_field_log2;
if (flags & (HIST_FIELD_FL_LOG2 | HIST_FIELD_FL_BUCKET)) {
unsigned long fl = flags & ~(HIST_FIELD_FL_LOG2 | HIST_FIELD_FL_BUCKET);
hist_field->fn = flags & HIST_FIELD_FL_LOG2 ? hist_field_log2 :
hist_field_bucket;
hist_field->operands[0] = create_hist_field(hist_data, field, fl, NULL);
hist_field->size = hist_field->operands[0]->size;
hist_field->type = kstrdup(hist_field->operands[0]->type, GFP_KERNEL);
Expand Down Expand Up @@ -1953,7 +1980,7 @@ static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,

static struct ftrace_event_field *
parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
char *field_str, unsigned long *flags)
char *field_str, unsigned long *flags, unsigned long *buckets)
{
struct ftrace_event_field *field = NULL;
char *field_name, *modifier, *str;
Expand All @@ -1980,7 +2007,22 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
*flags |= HIST_FIELD_FL_LOG2;
else if (strcmp(modifier, "usecs") == 0)
*flags |= HIST_FIELD_FL_TIMESTAMP_USECS;
else {
else if (strncmp(modifier, "bucket", 6) == 0) {
int ret;

modifier += 6;

if (*modifier == 's')
modifier++;
if (*modifier != '=')
goto error;
modifier++;
ret = kstrtoul(modifier, 0, buckets);
if (ret || !(*buckets))
goto error;
*flags |= HIST_FIELD_FL_BUCKET;
} else {
error:
hist_err(tr, HIST_ERR_BAD_FIELD_MODIFIER, errpos(modifier));
field = ERR_PTR(-EINVAL);
goto out;
Expand Down Expand Up @@ -2049,6 +2091,7 @@ static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
char *s, *ref_system = NULL, *ref_event = NULL, *ref_var = str;
struct ftrace_event_field *field = NULL;
struct hist_field *hist_field = NULL;
unsigned long buckets = 0;
int ret = 0;

s = strchr(str, '.');
Expand Down Expand Up @@ -2086,7 +2129,7 @@ static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
} else
str = s;

field = parse_field(hist_data, file, str, flags);
field = parse_field(hist_data, file, str, flags, &buckets);
if (IS_ERR(field)) {
ret = PTR_ERR(field);
goto out;
Expand All @@ -2097,6 +2140,7 @@ static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
ret = -ENOMEM;
goto out;
}
hist_field->buckets = buckets;

return hist_field;
out:
Expand Down Expand Up @@ -4698,6 +4742,11 @@ static void hist_trigger_print_key(struct seq_file *m,
} else if (key_field->flags & HIST_FIELD_FL_LOG2) {
seq_printf(m, "%s: ~ 2^%-2llu", field_name,
*(u64 *)(key + key_field->offset));
} else if (key_field->flags & HIST_FIELD_FL_BUCKET) {
unsigned long buckets = key_field->buckets;
uval = *(u64 *)(key + key_field->offset);
seq_printf(m, "%s: ~ %llu-%llu", field_name,
uval, uval + buckets -1);
} else if (key_field->flags & HIST_FIELD_FL_STRING) {
seq_printf(m, "%s: %-50s", field_name,
(char *)(key + key_field->offset));
Expand Down Expand Up @@ -5137,6 +5186,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
seq_printf(m, ".%s", flags);
}
}
if (hist_field->buckets)
seq_printf(m, "=%ld", hist_field->buckets);
}

static int event_hist_trigger_print(struct seq_file *m,
Expand Down

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