linux-kernel - Re: [PATCH] ftrace: Show timings of how long nop patching took

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Message-ID: <20241201150406.17f10247@rorschach.local.home>
Date: Sun, 1 Dec 2024 15:04:06 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Mike Rapoport <rppt@...nel.org>, Peter
 Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace: Show timings of how long nop patching took

On Sun, 1 Dec 2024 20:37:42 +0100
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> Hi Steven,
> 
> Le 17/10/2024 à 17:31, Steven Rostedt a écrit :
> > From: Steven Rostedt <rostedt@...dmis.org>
> > 
> > Since the beginning of ftrace, the code that did the patching had its
> > timings saved on how long it took to complete. But this information was
> > never exposed. It was used for debugging and exposing it was always
> > something that was on the TODO list. Now it's time to expose it. There's
> > even a file that is where it should go!
> > 
> > Also include how long patching modules took as a separate value.
> > 
> >   # cat /sys/kernel/tracing/dyn_ftrace_total_info
> >   57680 pages:231 groups: 9
> >   ftrace boot update time = 14024666 (ns)
> >   ftrace module total update time = 126070 (ns)  
> 
> What is this supposed to report / measure ?
> 
> On powerpc I get:
> 
> 25850 pages:14 groups: 3
> ftrace boot update time = 0 (ns)
> ftrace module total update time = 0 (ns)

Hmm, does powerpc support "trace_clock_local()" at early boot? I
probably can just switch from using "ftrace_now()" to using
ktime_get_real_ts64(). Hmm.

-- Steve