linux-kernel - Re: [PATCH 3/7] rcu/trace: Add name of the source for gp

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Date:   Thu, 18 Jun 2020 20:01:38 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org, "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: Re: [PATCH 3/7] rcu/trace: Add name of the source for gp_seq

On Thu, 18 Jun 2020 15:19:01 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> For future reference, the TPS() around strings is not optional.  Without
> it, trace messages from crash dumps are garbled, if I remember correctly.

When you pass in a string like this, only the pointer to the string is
saved in the ring buffer. User space tools have no idea what those
pointers are. The TPS() around strings maps those pointers to the
string and shows them in the /sys/kernel/tracing/printk_formats file,
such that perf and trace-cmd know how to make sense of those strings.

-- Steve