linux-kernel - Re: [RFC][PATCH] tracing: Allow creating instances with specified system events

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Message-ID: <o7zzg7i5jpso2x5rp3mawsjja3j52lomqyx2k2jgp54nrtf4gc@qhqv2ubkvubf>
Date:   Tue, 28 Nov 2023 09:49:14 +0100
From:   Daniel Wagner <dwagner@...e.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        dmaluka@...gle.com, Sean Paul <seanpaul@...omium.org>,
        Arun Easi <aeasi@...vell.com>
Subject: Re: [RFC][PATCH] tracing: Allow creating instances with specified
 system events

On Mon, Nov 27, 2023 at 05:50:21PM -0500, Steven Rostedt wrote:
> On Mon, 27 Nov 2023 17:41:08 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> > 
> > A trace instance may only need to enable specific events. As the eventfs
> > directory of an instance currently creates all events which adds overhead,
> > allow internal instances to be created with just the events in systems
> > that they care about. This currently only deals with systems and not
> > individual events, but this should bring down the overhead of creating
> > instances for specific use cases quite bit.
> 
> This change log is not very good. I didn't actually state what was done :-p
> 
> Anyway, function trace_array_get_by_name() has an added parameter "systems"
> (and I forgot to update its kerneldoc). This parameter is a string of
> comma, or space, or commas and spaces deliminators of event system names.
> If it's not NULL, then it will only create the event system directories of
> those event systems that match the systems parameter.
> 
> That is:
> 
>  trace_array_get_by_name("qla2xxx", "qla");
> 
> Will create an instance called "qla2xxx" and only have "qla" system events
> in it.

Makes sense to me. The qla2xxx driver is interested only in its own
trace events. This should be fine, at least as far I understand it.