From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752415AbdLLOou (ORCPT ); Tue, 12 Dec 2017 09:44:50 -0500 Received: from mail-pg0-f67.google.com ([74.125.83.67]:41107 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752299AbdLLOos (ORCPT ); Tue, 12 Dec 2017 09:44:48 -0500 X-Google-Smtp-Source: ACJfBouIYcLUcxbEzsGB/1fBLjBGa3IVbkKrd3u3LJ3NurkMRX8UUZwjCUbwYAIneWdD2pa0qXXKHw== Date: Tue, 12 Dec 2017 23:42:01 +0900 From: Namhyung Kim To: Tom Zanussi Cc: rostedt@goodmis.org, tglx@linutronix.de, mhiramat@kernel.org, vedang.patel@intel.com, bigeasy@linutronix.de, joel.opensrc@gmail.com, joelaf@google.com, mathieu.desnoyers@efficios.com, baohong.liu@intel.com, rajvi.jingar@intel.com, julia@ni.com, fengguang.wu@intel.com, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, kernel-team@lge.com Subject: Re: [PATCH v7 24/37] tracing: Add support for 'synthetic' events Message-ID: <20171212144201.GA21538@danjae.aot.lge.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > [fix noderef.cocci warnings, sizeof pointer for kcalloc of event->fields] > Signed-off-by: Fengguang Wu > --- [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] ? 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); > +}