linux-kernel - Re: [PATCH 17/17] libtracefs: Add man page for tracefs

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Message-ID: <YQqHxQ5XH/ZN5yUq@lx-t490>
Date:   Wed, 4 Aug 2021 14:27:49 +0200
From:   "Ahmed S. Darwish" <a.darwish@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Zanussi <zanussi@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 17/17] libtracefs: Add man page for tracefs_sql()

On Sun, Aug 01, 2021, Steven Rostedt wrote:
> On Sun, 1 Aug 2021 15:39:25 +0200
> "Ahmed S. Darwish" <a.darwish@...utronix.de> wrote:
>
> > On Fri, Jul 30, 2021, Steven Rostedt wrote:
> > > +
> > > +The SQL format is as follows:
> > > +
> > > +*SELECT* <fields> FROM <start-event> JOIN <end-event> ON <matching-fields> WHERE <filter>
> > > +
> > > +Note, although the examples show the SQL commands in uppercase, they are not required to
> > > +be so. That is, you can use "SELECT" or "select" or "sElEct".
> > > +
> >
> > Maybe it would be helpful to mention that, unlike normal SELECT queries,
> > the JOIN and ON parts above are _not_ optional?
> >
> > That is, generic "one event source" queries:
> >
> >   SELECT common_pid,msr,val FROM write_msr WHERE msr=72
> >
> > are not supported. (I wish they were though ;-))
>
> Actually, the sql parser should support it, but it will fail on the
> creation of events. That's because I started trying to make this create
> normal histograms. The problem is, that it can't really do a 1 to 1 on
> histograms and selects, so I gave up. But perhaps for the subset it can
> create, maybe I can still have it do so. That may require changing the
> API slightly.
>
> I'm not a big SQL person, so I don't know all the magic and I have no
> idea how to add the "values" part of the hist trigger.
>

Thanks! I've replied at the v2 thread.

(Discovered after-the-fact that a v3 was already sent, sorry..)

--
Ahmed S. Darwish
Linutronix GmbH