linux-kernel - Re: [PATCH v5 4/4] tracing/Documentation: Add a section about backup instance

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Message-ID: <20260129151900.44b6182c@gandalf.local.home>
Date: Thu, 29 Jan 2026 15:19:00 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] tracing/Documentation: Add a section about
 backup instance

On Wed, 28 Jan 2026 09:10:11 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Add a section about backup instance to the debugging.rst.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  Documentation/trace/debugging.rst |   19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/Documentation/trace/debugging.rst b/Documentation/trace/debugging.rst
> index 4d88c346fc38..73e2154bcf98 100644
> --- a/Documentation/trace/debugging.rst
> +++ b/Documentation/trace/debugging.rst
> @@ -159,3 +159,22 @@ If setting it from the kernel command line, it is recommended to also
>  disable tracing with the "traceoff" flag, and enable tracing after boot up.
>  Otherwise the trace from the most recent boot will be mixed with the trace
>  from the previous boot, and may make it confusing to read.
> +
> +Using a backup instance for keeping previous boot data
> +------------------------------------------------------
> +
> +It is also possible to record trace data at system boot time by specifying
> +events with the persistent ring buffer, but in this case the data before the
> +reboot will be lost before it can be read. This problem can be solved by a
> +backup instance. From the kernel command line::
> +
> +  reserve_mem=12M:4096:trace trace_instance=boot_map@...ce,sched,irq trace_instance=backup=boot_map
> +
> +When the boot up, the previous data in the`boot_map` is copied to "backup"

  s/When the boot up/On boot up/                   copied to the "backup"

> +instance, and the "sched:*" and "irq:*" events for current boot are traced on

                                                  for the current boot are traced in


> +"boot_map". Thus user can read the previous boot data from the "backup" instance

               Thus the user

> +without stopping trace.

           stopping the trace.

> +
> +Note that this "backup" instance is readonly, and will be removed automatically
> +if you clear the trace data or read out all trace data from "trace_pipe" or
> +"trace_pipe_raw" files.
> \ No newline at end of file

Definite articles are a pain ;-)

-- Steve