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SubjectRe: [PATCH v2 32/40] tracing: Add cpu field for hist triggers
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On Fri, 2017-09-08 at 15:08 -0400, Steven Rostedt wrote:
> On Tue, 5 Sep 2017 16:57:44 -0500
> Tom Zanussi <tom.zanussi@linux.intel.com> wrote:
>
> > A common key to use in a histogram is the cpuid - add a new cpu
> > 'synthetic' field for that purpose. This field is named cpu rather
> > than $cpu or $common_cpu because 'cpu' already exists as a special
> > filter field and it makes more sense to match that rather than add
> > another name for the same thing.
> >
> > Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> > ---
> > Documentation/trace/events.txt | 18 ++++++++++++++++++
> > kernel/trace/trace_events_hist.c | 30 +++++++++++++++++++++++++++---
> > 2 files changed, 45 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
> > index 2cc08d4..9717688 100644
> > --- a/Documentation/trace/events.txt
> > +++ b/Documentation/trace/events.txt
> > @@ -668,6 +668,24 @@ The following commands are supported:
> > The examples below provide a more concrete illustration of the
> > concepts and typical usage patterns discussed above.
> >
> > + 'synthetic' event fields
> > + ------------------------
> > +
> > + There are a number of 'synthetic fields' available for use as keys
> > + or values in a hist trigger. These look like and behave as if they
> > + were event fields, but aren't actually part of the event's field
> > + definition or format file. They are however available for any
> > + event, and can be used anywhere an actual event field could be.
> > + 'Synthetic' field names are always prefixed with a '$' character to
> > + indicate that they're not normal fields (with the exception of
> > + 'cpu', for compatibility with existing filter usage):
> > +
> > + $common_timestamp u64 - timestamp (from ring buffer) associated
> > + with the event, in nanoseconds. May be
> > + modified by .usecs to have timestamps
> > + interpreted as microseconds.
>
> I guess the above should have been added with the synthetic field
> addition.
>

Yeah, somehow this bit got shuffled to the wrong place refactoring the
patches.

> > + cpu int - the cpu on which the event occurred.
>
> Then this (and the explanation of '$' for cpu above) should be added
> with this patch.
>

Yep, will do.

>
> > +
> >
> > 6.2 'hist' trigger examples
> > ---------------------------
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index 4f66f2e..0782766 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -226,6 +226,7 @@ enum hist_field_flags {
> > HIST_FIELD_FL_VAR_ONLY = 8192,
> > HIST_FIELD_FL_EXPR = 16384,
> > HIST_FIELD_FL_VAR_REF = 32768,
> > + HIST_FIELD_FL_CPU = 65536,
> > };
> >
> > struct var_defs {
> > @@ -1170,6 +1171,16 @@ static u64 hist_field_timestamp(struct hist_field *hist_field,
> > return ts;
> > }
> >
> > +static u64 hist_field_cpu(struct hist_field *hist_field,
> > + struct tracing_map_elt *elt,
> > + struct ring_buffer_event *rbe,
> > + void *event)
> > +{
> > + int cpu = raw_smp_processor_id();
>
> Hmm, I wonder if this should be just smp_processor_id(). Why have the
> raw_?
>

You're right, smp_processor_id() should be fine.

> > +
> > + return cpu;
> > +}
> > +
> > static struct hist_field *check_var_ref(struct hist_field *hist_field,
> > struct hist_trigger_data *var_data,
> > unsigned int var_idx)
> > @@ -1518,6 +1529,8 @@ static const char *hist_field_name(struct hist_field *field,
> > field_name = hist_field_name(field->operands[0], ++level);
> > else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
> > field_name = "$common_timestamp";
> > + else if (field->flags & HIST_FIELD_FL_CPU)
> > + field_name = "cpu";
> > else if (field->flags & HIST_FIELD_FL_EXPR ||
> > field->flags & HIST_FIELD_FL_VAR_REF)
> > field_name = field->name;
> > @@ -1990,6 +2003,15 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
> > goto out;
> > }
> >
> > + if (flags & HIST_FIELD_FL_CPU) {
> > + hist_field->fn = hist_field_cpu;
> > + hist_field->size = sizeof(int);
> > + hist_field->type = kstrdup("int", GFP_KERNEL);
> > + if (!hist_field->type)
> > + goto free;
> > + goto out;
> > + }
> > +
> > if (WARN_ON_ONCE(!field))
> > goto out;
> >
> > @@ -2182,7 +2204,9 @@ static struct hist_field *parse_var_ref(struct trace_array *tr,
> > hist_data->enable_timestamps = true;
> > if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
> > hist_data->attrs->ts_in_usecs = true;
> > - } else {
> > + } else if (strcmp(field_name, "cpu") == 0)
> > + *flags |= HIST_FIELD_FL_CPU;
> > + else {
> > field = trace_find_event_field(file->event_call, field_name);
> > if (!field || !field->size) {
> > field = ERR_PTR(-EINVAL);
>
>
> > @@ -3185,7 +3209,6 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
> > goto out;
> > }
> > }
> > -
> > if (param[0] == '$')
> > hist_field = onmatch_find_var(hist_data, data, system,
> > event_name, param);
> > @@ -3200,7 +3223,6 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
> > ret = -EINVAL;
> > goto out;
> > }
> > -
>
> Why the modification of whitespace here?
>

Again no good reason, another casualty of refactoring lots of
patches ;-)

Tom


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