Hi Namhyung,
On Tue, 2017-12-12 at 23:42 +0900, Namhyung Kim wrote:
> On Wed, Dec 06, 2017 at 04:38:05PM -0600, Tom Zanussi wrote:
> > Synthetic events are user-defined events generated from hist trigger
> > variables saved from one or more other events.
> >
> > To define a synthetic event, the user writes a simple specification
> > consisting of the name of the new event along with one or more
> > variables and their type(s), to the tracing/synthetic_events file.
> >
> > For instance, the following creates a new event named 'wakeup_latency'
> > with 3 fields: lat, pid, and prio:
> >
> > # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
> > /sys/kernel/debug/tracing/synthetic_events
> >
> > Reading the tracing/synthetic_events file lists all the
> > currently-defined synthetic events, in this case the event we defined
> > above:
> >
> > # cat /sys/kernel/debug/tracing/synthetic_events
> > wakeup_latency u64 lat; pid_t pid; int prio
> >
> > At this point, the synthetic event is ready to use, and a histogram
> > can be defined using it:
> >
> > # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
> > /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
> >
> > The new event is created under the tracing/events/synthetic/ directory
> > and looks and behaves just like any other event:
> >
> > # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
> > enable filter format hist id trigger
> >
> > Although a histogram can be defined for it, nothing will happen until
> > an action tracing that event via the trace_synth() function occurs.
> > The trace_synth() function is very similar to all the other trace_*
> > invocations spread throughout the kernel, except in this case the
> > trace_ function and its corresponding tracepoint isn't statically
> > generated but defined by the user at run-time.
> >
> > How this can be automatically hooked up via a hist trigger 'action' is
> > discussed in a subsequent patch.
> >
> > Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> > [fix noderef.cocci warnings, sizeof pointer for kcalloc of event->fields]
> > Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
> > ---
>
> [SNIP]
> > +static enum print_line_t print_synth_event(struct trace_iterator *iter,
> > + int flags,
> > + struct trace_event *event)
> > +{
> > + struct trace_array *tr = iter->tr;
> > + struct trace_seq *s = &iter->seq;
> > + struct synth_trace_event *entry;
> > + struct synth_event *se;
> > + unsigned int i, n_u64;
> > + char print_fmt[32];
> > + const char *fmt;
> > +
> > + entry = (struct synth_trace_event *)iter->ent;
> > + se = container_of(event, struct synth_event, call.event);
> > +
> > + trace_seq_printf(s, "%s: ", se->name);
> > +
> > + for (i = 0, n_u64 = 0; i < se->n_fields; i++) {
> > + if (trace_seq_has_overflowed(s))
> > + goto end;
> > +
> > + fmt = synth_field_fmt(se->fields[i]->type);
> > +
> > + /* parameter types */
> > + if (tr->trace_flags & TRACE_ITER_VERBOSE)
> > + trace_seq_printf(s, "%s ", fmt);
> > +
> > + snprintf(print_fmt, sizeof(print_fmt), "%%s=%s%%s", fmt);
> > +
> > + /* parameter values */
> > + if (se->fields[i]->is_string) {
> > + trace_seq_printf(s, print_fmt, se->fields[i]->name,
> > + (char *)(long)entry->fields[n_u64],
>
> Hmm.. shouldn't it be (char *)&entry->fields[n_u64] ?
>
Yes, thanks for pointing this out - looks like I need to add something
that enables string-containing synthetic events and looks at the trace
file display to my testing..
Tom
> Thanks,
> Namhyung
>
>
> > + i == se->n_fields - 1 ? "" : " ");
> > + n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
> > + } else {
> > + trace_seq_printf(s, print_fmt, se->fields[i]->name,
> > + entry->fields[n_u64],
> > + i == se->n_fields - 1 ? "" : " ");
> > + n_u64++;
> > + }
> > + }
> > +end:
> > + trace_seq_putc(s, '\n');
> > +
> > + return trace_handle_return(s);
> > +}
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