linux-kernel - Re: [PATCH 2/2 v8] printk: Add monotonic, boottime, and realtime timestamps

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Date:   Fri, 25 Aug 2017 10:58:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     John Stultz <john.stultz@...aro.org>,
        Joel Fernandes <joelaf@...gle.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoffer Dall <cdall@...aro.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Olof Johansson <olof@...om.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2 v8] printk: Add monotonic, boottime, and realtime
 timestamps

On Fri, 25 Aug 2017 10:46:21 -0400
Prarit Bhargava <prarit@...hat.com> wrote:


> np.  I'm going to copy the code for
> 
> u64 notrace ktime_get_boot_fast_ns(void)
> 
> but I'm unsure why the function is marked "notrace", and if
> __ktime_get_real_fast_ns_unsafe() must be as well?  I don't see anything in the
> git log that indicates why the function is notrace.
> 
> I've added Joel to this thread ...

The "notrace" is added because it is one of the trace clocks:

kernel/trace/trace.c:   { ktime_get_boot_fast_ns,       "boot",         1 },

And function tracer can use it. We don't want to be tracing the clock
that the function tracer is using (otherwise it will get double
traced). It use to bug, but I believe I finally got the recursion
protection working to prevent that.

-- Steve