Date:   Fri, 11 Jan 2019 10:25:40 -0600
From:   Tom Zanussi <zanussi@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        julia@...com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v11 10/15] tracing: Add alternative synthetic event
 trace action syntax

Hi Namhyung,

On Fri, 2019-01-11 at 15:07 +0900, Namhyung Kim wrote:
> On Wed, Jan 09, 2019 at 01:49:17PM -0600, Tom Zanussi wrote:
> > From: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > 
> > Add a 'trace(synthetic_event_name, params)' alternative to
> > synthetic_event_name(params).
> > 
> > Currently, the syntax used for generating synthetic events is to
> > invoke synthetic_event_name(params) i.e. use the synthetic event
> > name
> > as a function call.
> > 
> > Users requested a new form that more explicitly shows that the
> > synthetic event is in effect being traced.  In this version, a new
> > 'trace()' keyword is used, and the synthetic event name is passed
> > in
> > as the first argument.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > ---
> >  Documentation/trace/histogram.rst | 21 ++++++++++++++++++++
> >  kernel/trace/trace.c              |  1 +
> >  kernel/trace/trace_events_hist.c  | 42
> > +++++++++++++++++++++++++++++++++++----
> >  3 files changed, 60 insertions(+), 4 deletions(-)
> > 
> > diff --git a/Documentation/trace/histogram.rst
> > b/Documentation/trace/histogram.rst
> > index 79476c906b1a..4939bad1c1cd 100644
> > --- a/Documentation/trace/histogram.rst
> > +++ b/Documentation/trace/histogram.rst
> > @@ -1874,6 +1874,7 @@ The available handlers are:
> >  The available actions are:
> >  
> >    - <synthetic_event_name>(param list)         - generate
> > synthetic event
> > +  - trace(<synthetic_event_name>,(param list)) - generate
> > synthetic event
> 
> Shouldn't it be
> 
> 	"trace(<synthetic_event_name>,param list)"
> 
> ?  Otherwise it looks like we need two parentheses.

Good point, I'll remove the params.

> 
> IMHO, it seems better for consistency using this new syntax only.
> Of course it should support the old syntax as well for compatibility
> (and maybe make it undocumented?).  But I won't insist strongly..
> 

OK, yeah, I really hate when things are undocumented, so I think
removing the documentation would be a step backward, but maybe changing
the emphasis to the trace() form would suffice.  How about the below?:


diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index e5bcef360997..0ea59d45aef1 100644
--- a/Documentation/trace/histogram.rst
+++ b/Documentation/trace/histogram.rst
@@ -1873,46 +1873,45 @@ The available handlers are:
 
 The available actions are:
 
-  - <synthetic_event_name>(param list)         - generate synthetic event
   - trace(<synthetic_event_name>,param list)   - generate synthetic event
   - save(field,...)                            - save current event fields
   - snapshot()                                 - snapshot the trace buffer
 
 The following commonly-used handler.action pairs are available:
 
-  - onmatch(matching.event).<synthetic_event_name>(param list)
-
-    or
-
   - onmatch(matching.event).trace(<synthetic_event_name>,param list)
 
-    The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
-    trigger action is invoked whenever an event matches and the
-    histogram entry would be added or updated.  It causes the named
-    synthetic event to be generated with the values given in the
+    The 'onmatch(matching.event).trace(<synthetic_event_name>,param
+    list)' hist trigger action is invoked whenever an event matches
+    and the histogram entry would be added or updated.  It causes the
+    named synthetic event to be generated with the values given in the
     'param list'.  The result is the generation of a synthetic event
     that consists of the values contained in those variables at the
-    time the invoking event was hit.
-
-    There are two equivalent forms available for generating synthetic
-    events.  In the first form, the synthetic event name is used as if
-    it were a function name.  For example, if the synthetic event name
-    is 'wakeup_latency', the wakeup_latency event would be generated
-    by invoking it as if it were a function call, with the event field
-    values passed in as arguments: wakeup_latency(arg1,arg2).  The
-    second form simply uses the 'trace' keyword as the function name
-    and passes in the synthetic event name as the first argument,
-    followed by the field values: trace(wakeup_latency,arg1,arg2).
-
-    The 'param list' consists of one or more parameters which may be
-    either variables or fields defined on either the 'matching.event'
-    or the target event.  The variables or fields specified in the
-    param list may be either fully-qualified or unqualified.  If a
-    variable is specified as unqualified, it must be unique between
-    the two events.  A field name used as a param can be unqualified
-    if it refers to the target event, but must be fully qualified if
-    it refers to the matching event.  A fully-qualified name is of the
-    form 'system.event_name.$var_name' or 'system.event_name.field'.
+    time the invoking event was hit.  For example, if the synthetic
+    event name is 'wakeup_latency', a wakeup_latency event is
+    generated using onmatch(event).trace(wakeup_latency,arg1,arg2).
+
+    There is also an equivalent alternative form available for
+    generating synthetic events.  In this form, the synthetic event
+    name is used as if it were a function name.  For example, using
+    the 'wakeup_latency' synthetic event name again, the
+    wakeup_latency event would be generated by invoking it as if it
+    were a function call, with the event field values passed in as
+    arguments: onmatch(event).wakeup_latency(arg1,arg2).  The syntax
+    for this form is:
+
+      onmatch(matching.event).<synthetic_event_name>(param list)
+
+    In either case, the 'param list' consists of one or more
+    parameters which may be either variables or fields defined on
+    either the 'matching.event' or the target event.  The variables or
+    fields specified in the param list may be either fully-qualified
+    or unqualified.  If a variable is specified as unqualified, it
+    must be unique between the two events.  A field name used as a
+    param can be unqualified if it refers to the target event, but
+    must be fully qualified if it refers to the matching event.  A
+    fully-qualified name is of the form 'system.event_name.$var_name'
+    or 'system.event_name.field'.
 
     The 'matching.event' specification is simply the fully qualified
     event name of the event that matches the target event for the
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 84981b61d45f..8c220d97c214 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4899,7 +4899,6 @@ static const char readme_msg[] =
 	"\t        onmax(var)               - invoke if var exceeds current max\n"
 	"\t        onchange(var)            - invoke action if var changes\n\n"
 	"\t    The available actions are:\n\n"
-	"\t        <synthetic_event>(param list)        - generate synthetic event\n"
 	"\t        trace(<synthetic_event>,param list)  - generate synthetic event\n"
 	"\t        save(field,...)                      - save current event fields\n"
 	"\t        snapshot()                           - snapshot the trace buffer\n"

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