On Tue, 31 Mar 2026 17:21:05 -0400 Steven Rostedt <[email protected]> wrote:
> On Wed, 1 Apr 2026 01:32:41 +0900 > "Masami Hiramatsu (Google)" <[email protected]> wrote: > > > From: Masami Hiramatsu (Google) <[email protected]> > > > > Add a section about backup instance to the debugging.rst. > > > > Signed-off-by: Masami Hiramatsu (Google) <[email protected]> > > --- > > Changes in v6: > > - Fix typos. > > --- > > Documentation/trace/debugging.rst | 19 +++++++++++++++++++ > > 1 file changed, 19 insertions(+) > > > > diff --git a/Documentation/trace/debugging.rst > > b/Documentation/trace/debugging.rst > > index 4d88c346fc38..15857951b506 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@trace,sched,irq > > trace_instance=backup=boot_map > > The above didn't actually work well without my patch to enable events on > the persistent ring buffer with the backup. But keep it, as it will work > with my patch ;-) Ah, thanks! Let me rebase on it. > > -- Steve > > > > + > > +On boot up, the previous data in the "boot_map" is copied to the "backup" > > +instance, and the "sched:*" and "irq:*" events for the current boot are > > traced > > +in the "boot_map". Thus the user can read the previous boot data from the > > "backup" > > +instance without 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 the > > "trace_pipe" > > +or the "trace_pipe_raw" files. > > \ No newline at end of file > -- Masami Hiramatsu (Google) <[email protected]>
