linux-kernel - Re: [patch 4/9] Remove the TSC synchronization on SMP machines

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Message-Id: <1171356078.12771.47.camel@laptopd505.fenrus.org>
Date:	Tue, 13 Feb 2007 09:41:17 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Christoph Lameter <clameter@....com>,
	Vojtech Pavlik <vojtech@...e.cz>, Jiri Bohac <jbohac@...e.cz>,
	linux-kernel@...r.kernel.org, ssouhlal@...ebsd.org,
	tglx@...utronix.de, johnstul@...ibm.com, zippel@...ux-m68k.org,
	andrea@...e.de
Subject: Re: [patch 4/9] Remove the TSC synchronization on SMP machines

On Tue, 2007-02-13 at 09:28 +0100, Andi Kleen wrote:
> On Tuesday 13 February 2007 07:40, Arjan van de Ven wrote:
> > On Mon, 2007-02-12 at 16:34 -0800, Christoph Lameter wrote:
> > > On Fri, 2 Feb 2007, Andi Kleen wrote:
> > > 
> > > > I've threatened to just disable RDTSC for ring 3 before, but it'll likely
> > > > never happen because too many programs use it.
> > > 
> > > Those programs are aware that they are fiddling around with low level 
> > > material but with this patchset we are going to have a non 
> > > monotonic time subsystem?
> > 
> > no quite the opposite. gettimeofday() currently is NOT monotonic
> > unfortunately. 
> 
> Anytime it is non monotonic that's a bug. We've had bugs
> like this before, but recently we're doing reasonably well. Of course
> there can be always improvements, but in general I don't agree
> with your statement, sorry. You can usually rely on it being monotonic,
> short of the known limitations (e.g. don't run ntpd) 

oh I agree it should be monotonic, but I remember an argument I had with
you several weeks ago where you were basically saying the opposite ;)

I'm happy to see gtod become more monotonic/reliable any way we can


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
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