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SubjectRe: [PATCH] tracing: Add "grouping" to histogram logic
On Sat, 3 Jul 2021 19:07:25 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> On Fri, 2 Jul 2021 17:56:48 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> >
> > 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.
>
> Great! So is that a kind of "unit" of the keys?

Not sure if "unit" is the write word. Just a division.

>
> > 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.
> >
> > Introduce a "grouping" command to each field where it will record in a
> > rounded number. For example:
>
> BTW, the separator seems a bit confusing. Is it "keys=FIELD-UNIT"?
> I prefer to use '/' as "keys=FIELD/UNIT" so that the FIELD is
> grouped by UNIT units. What would you think?

Yeah, I just picked '-' but then realized it would conflict with other
key words.

>
> Also, could you also update README file?

Agreed. BTW, I forgot to add [RFC] to the subject, because that's what
this patch is.

Thanks!

-- Steve


>
> Thank you,
>
> >
> > ># echo 'hist:keys=bytes_req-100:sort=bytes_req' > events/kmem/kmalloc/trigger
> > ># cat events/kmem/kmalloc/hist
> > # event histogram
> > #
> > # trigger info:
> > hist:keys=bytes_req-100:vals=hitcount:sort=bytes_req-100:size=2048
> > [active]
> > #
> >
> > { bytes_req: 0-99 } hitcount: 7207
> > { bytes_req: 100-199 } hitcount: 1030
> > { bytes_req: 200-299 } hitcount: 602
> > { bytes_req: 300-399 } hitcount: 414
> > { bytes_req: 400-499 } hitcount: 584
> > { bytes_req: 500-599 } hitcount: 35
> > { bytes_req: 600-699 } hitcount: 361
> > { bytes_req: 700-799 } hitcount: 37
> > { bytes_req: 800-899 } hitcount: 26
> > { bytes_req: 900-999 } hitcount: 15
> > { bytes_req: 1100-1199 } hitcount: 4
> > { bytes_req: 1200-1299 } hitcount: 102
> > { bytes_req: 1300-1399 } hitcount: 2
> > { bytes_req: 1400-1499 } hitcount: 15
> > { bytes_req: 1500-1599 } hitcount: 100
> > { bytes_req: 1600-1699 } hitcount: 1
> > { bytes_req: 1700-1799 } hitcount: 3
> > { bytes_req: 1800-1899 } hitcount: 10
> > { bytes_req: 2000-2099 } hitcount: 19
> > { bytes_req: 2100-2199 } hitcount: 3
> > { bytes_req: 2500-2599 } hitcount: 72
> > { bytes_req: 2900-2999 } hitcount: 1
> > { bytes_req: 3300-3399 } hitcount: 4
> > { bytes_req: 3900-3999 } hitcount: 2
> > { bytes_req: 4000-4099 } hitcount: 1761
> > { bytes_req: 4600-4699 } hitcount: 65
> > { bytes_req: 5000-5099 } hitcount: 3
> > { bytes_req: 6500-6599 } hitcount: 1
> > { bytes_req: 8100-8199 } hitcount: 1
> > { bytes_req: 9800-9899 } hitcount: 1
> >
> > Totals:
> > Hits: 12481
> > Entries: 30
> > Dropped: 0
> >
> > This finally makes the histograms actual histograms!
> >
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > ---
> > kernel/trace/trace_events_hist.c | 34 ++++++++++++++++++++++++++++----
> > 1 file changed, 30 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index ba03b7d84fc2..d6e644df9506 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -120,6 +120,7 @@ struct hist_field {
> > unsigned int size;
> > unsigned int offset;
> > unsigned int is_signed;
> > + unsigned long grouping;
> > const char *type;
> > struct hist_field *operands[HIST_FIELD_OPERANDS_MAX];
> > struct hist_trigger_data *hist_data;
> > @@ -3761,6 +3762,7 @@ static int create_key_field(struct hist_trigger_data *hist_data,
> > {
> > struct trace_array *tr = hist_data->event_file->tr;
> > struct hist_field *hist_field = NULL;
> > + char *field;
> > unsigned long flags = 0;
> > unsigned int key_size;
> > int ret = 0;
> > @@ -3768,14 +3770,16 @@ static int create_key_field(struct hist_trigger_data *hist_data,
> > if (WARN_ON(key_idx >= HIST_FIELDS_MAX))
> > return -EINVAL;
> >
> > + field = strsep(&field_str, "-");
> > +
> > flags |= HIST_FIELD_FL_KEY;
> >
> > - if (strcmp(field_str, "stacktrace") == 0) {
> > + if (strcmp(field, "stacktrace") == 0) {
> > flags |= HIST_FIELD_FL_STACKTRACE;
> > key_size = sizeof(unsigned long) * HIST_STACKTRACE_DEPTH;
> > hist_field = create_hist_field(hist_data, NULL, flags, NULL);
> > } else {
> > - hist_field = parse_expr(hist_data, file, field_str, flags,
> > + hist_field = parse_expr(hist_data, file, field, flags,
> > NULL, 0);
> > if (IS_ERR(hist_field)) {
> > ret = PTR_ERR(hist_field);
> > @@ -3783,7 +3787,7 @@ static int create_key_field(struct hist_trigger_data *hist_data,
> > }
> >
> > if (field_has_hist_vars(hist_field, 0)) {
> > - hist_err(tr, HIST_ERR_INVALID_REF_KEY, errpos(field_str));
> > + hist_err(tr, HIST_ERR_INVALID_REF_KEY, errpos(field));
> > destroy_hist_field(hist_field, 0);
> > ret = -EINVAL;
> > goto out;
> > @@ -3792,6 +3796,14 @@ static int create_key_field(struct hist_trigger_data *hist_data,
> > key_size = hist_field->size;
> > }
> >
> > + if (field_str) {
> > + unsigned long grouping;
> > +
> > + ret = kstrtoul(field_str, 0, &grouping);
> > + if (!ret)
> > + hist_field->grouping = grouping;
> > + }
> > +
> > hist_data->fields[key_idx] = hist_field;
> >
> > key_size = ALIGN(key_size, sizeof(u64));
> > @@ -4548,8 +4560,18 @@ static void event_hist_trigger(struct event_trigger_data *data,
> > if (key_field->flags & HIST_FIELD_FL_STRING) {
> > key = (void *)(unsigned long)field_contents;
> > use_compound_key = true;
> > - } else
> > + } else {
> > + if (key_field->grouping) {
> > + unsigned long grouping = key_field->grouping;
> > +
> > + if (field_contents >= LONG_MAX)
> > + field_contents = div64_ul(field_contents, grouping);
> > + else
> > + field_contents = (u64)((unsigned long)field_contents / grouping);
> > + field_contents *= grouping;
> > + }
> > key = (void *)&field_contents;
> > + }
> > }
> >
> > if (use_compound_key)
> > @@ -4663,6 +4685,8 @@ static void hist_trigger_print_key(struct seq_file *m,
> > } else {
> > uval = *(u64 *)(key + key_field->offset);
> > seq_printf(m, "%s: %10llu", field_name, uval);
> > + if (key_field->grouping)
> > + seq_printf(m, "-%llu", uval + key_field->grouping - 1);
> > }
> > }
> >
> > @@ -5096,6 +5120,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
> > seq_printf(m, ".%s", flags);
> > }
> > }
> > + if (hist_field->grouping)
> > + seq_printf(m, "-%ld", hist_field->grouping);
> > }
> >
> > static int event_hist_trigger_print(struct seq_file *m,
> > --
> > 2.31.1
> >
>
>

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