linux-kernel - Re: [PATCH] tracing: Record trace_clock in last_boot

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Message-Id: <20250417140957.d0051e19f562cb2b80a8e1c0@kernel.org>
Date: Thu, 17 Apr 2025 14:09:57 +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] tracing: Record trace_clock in last_boot_info

On Wed, 16 Apr 2025 11:12:27 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 16 Apr 2025 23:46:38 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > Record trace_clock information in the trace_scratch area and show
> > it via `last_boot_info` so that reader can docode the timestamp
> > correctly.
> > With this change, the first line of the last_boot_info becomes
> > trace_clock which is used when the trace was recorded. E.g.
> > 
> > /sys/kernel/tracing/instances/boot_mapped # cat last_boot_info
> > trace_clock: mono
> > ffffffff81000000        [kernel]
> > 
> 
> As this will not go in this cycle, which means tools may be built
> around this.
> 
> Either we put it at the end, or we make it:
> 
> # trace_clock: mono
> ffffffff81000000        [kernel]
> 
> Where "info" like "trace_clock" will be in the comment section, and all
> non comments will be addresses.

OK. Anyway, as we discussed offline, I'll update it to just set the
value to the "trace_clock" file instead of using "last_boot_info".

Thank you,

> 
> Tooling can then just ignore the comment section, or read it for more
> information.
> 
> -- Steve


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