linux-kernel - Re: [RFC PATCH 1/3] Unified trace buffer

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Date:	Thu, 25 Sep 2008 13:32:47 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
cc:	Ingo Molnar <mingo@...e.hu>, Martin Bligh <mbligh@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Martin Bligh <mbligh@...igh.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com, "Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Tom Zanussi <zanussi@...cast.net>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH 1/3] Unified trace buffer



On Thu, 25 Sep 2008, Mathieu Desnoyers wrote:

> * Steven Rostedt (rostedt@...dmis.org) wrote:
> > 
> > On Thu, 25 Sep 2008, Mathieu Desnoyers wrote:
> > > The problem with sched_clock is that it gives a 1 HZ timestamp accuracy
> > > for events happening across different CPUs. Within this 1 HZ range, it
> > > uses the TSC and clip when it reaches a max. Good enough for scheduler
> > > or for tracing events on a single CPU, but I think it is not exactly
> > > what we need to reorder events happening across CPUs.
> > > 
> > 
> > 
> > Hmm,
> > 
> > sched_clock gives ns accuracy unless the tsc is disabled. And in that 
> > case, we don't have any CPU clock :-/
> > 
> 
> Even on architectures with non-synchronized TSCs ?

Yep, even on those ;-)

-- Steve
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