linux-kernel - Re: [PATCH v7 02/13] user_events: Add minimal support for trace

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Message-ID: <20211210124305.24acd61f@gandalf.local.home>
Date:   Fri, 10 Dec 2021 12:43:05 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Beau Belgrave <beaub@...ux.microsoft.com>,
        linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 02/13] user_events: Add minimal support for
 trace_event into ftrace

On Fri, 10 Dec 2021 19:43:58 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> > +/* Limit how long of an event name plus args within the subsystem. */
> > +#define MAX_EVENT_DESC 512
> > +#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
> > +#define MAX_FIELD_ARRAY_SIZE (2 * PAGE_SIZE)  
> 
> I don't recommend to record the event which size is more than a page size...
> Maybe 256 entries?
> It is also better to limit the total size of the event and the number
> of fields (arguments).
> 
> Steve, can we write such a big event data on the trace buffer?

In the future yes!

  https://lore.kernel.org/all/20211125175253.186422-1-tz.stoyanov@gmail.com/

But it will still require some configuration changes from user space. But
that said, if the user wants to add a larger size, then they can do so (in
the future).

-- Steve