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

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Message-Id: <20260130222449.bc25b973597721b6a22e4f6d@kernel.org>
Date: Fri, 30 Jan 2026 22:24:49 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.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 Thu, 29 Jan 2026 15:19:00 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> 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"

Ah, thanks,

> 
> > +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

   ^ the "boot_map".

> 
>                Thus the user
> 
> > +without stopping trace.
> 
>            stopping the trace.

OK.

> 
> > +
> > +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 ;-)

Thanks!

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>