linux-kernel - Re: [PATCH 0/3] [RFC] init, tracing: Add initcall trace events

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Message-Id: <20180323125016.270ea1558fe2499b1a12bfd7@linux-foundation.org>
Date:   Fri, 23 Mar 2018 12:50:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Abderrahmane Benbachir <abderrahmane.benbachir@...ymtl.ca>,
        AmÃ©rico Wang <xiyou.wangcong@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/3] [RFC] init, tracing: Add initcall trace events

On Fri, 23 Mar 2018 11:02:41 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:

> A while ago we had a boot tracer. But it was eventually removed:
>  commit 30dbb20e68e6f ("tracing: Remove boot tracer").
> 
> The rational was because there is already a initcall_debug boot option
> that causes printk()s of all the initcall functions.

"rationale" :)

> The problem with the initcall_debug option is that printk() is awfully slow,
> and makes it difficult to see the real impact of initcalls. Mainly because
> a single printk() is usually slower than most initcall functions.

Not understanding this.  We do it correctly:

	calltime = ktime_get();
	ret = fn();
	rettime = ktime_get();

so the displayed initcall timing is independent of the printk()
execution time?