linux-kernel - Re: [RFC PATCH v2] ftrace: support very early function tracing

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Message-ID: <20171108193352.GM3326@worktop>
Date:   Wed, 8 Nov 2017 20:33:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Abderrahmane Benbachir <abderrahmane.benbachir@...ymtl.ca>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        mathieu.desnoyers@...icios.com,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH v2] ftrace: support very early function tracing

On Wed, Nov 08, 2017 at 02:19:07PM -0500, Steven Rostedt wrote:
> On Wed, 8 Nov 2017 20:07:27 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Depends on how early you need things; ideally you'd be able to use the
> 
> Well, he starts tracing at the entry of start_kernel(), would this
> handle that?

You'll have to run something first to initialize clocks in any case.
He's calling native_calibrate_cpu() (which of course if completely
broken for virt).

So you might as well setup the sched_clock() infra properly.