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Date: Wed, 8 Nov 2017 20:07:27 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Abderrahmane Benbachir <abderrahmane.benbachir@polymtl.ca>,
        linux-kernel@vger.kernel.org, mingo@redhat.com,
        mathieu.desnoyers@efficios.com, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH v2] ftrace: support very early function tracing
Message-ID: <20171108190727.GL3326@worktop>
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On Wed, Nov 08, 2017 at 11:07:57AM -0500, Steven Rostedt wrote:
> On Wed, 8 Nov 2017 09:10:58 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Tue, Nov 07, 2017 at 09:17:06PM -0500, Steven Rostedt wrote:
> > > > +#ifdef CONFIG_X86_TSC
> > > > +	entry->clock = rdtsc();
> > > > +#else
> > > > +	entry->clock = trace_clock_local();
> > > > +#endif  
> > 
> > > > +#ifdef CONFIG_X86_TSC
> > > > +	cpu_khz = native_calibrate_cpu();
> > > > +#endif  
> > 
> > > > +#ifdef CONFIG_X86_TSC
> > > > +		ns = cycles_to_ns(entry->clock, cpu_khz);
> > > > +#else
> > > > +		ns = entry->clock;
> > > > +#endif  
> > 
> > Yeah, no, not going to happen...
> 
> Agreed.

Depends on how early you need things; ideally you'd be able to use the
stuff from here:

  https://lkml.kernel.org/r/1504116205-355281-1-git-send-email-pasha.tatashin@oracle.com

That is, fix the normal time sources to work earlier instead of building
parallel infrastructure.