linux-kernel - Re: [PATCH] Turn rdmsr, rdtsc into inline functions, clarify names

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Message-ID: <20060807124855.GB21003@suse.cz>
Date:	Mon, 7 Aug 2006 14:48:55 +0200
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Andi Kleen <ak@....de>
Cc:	Dmitry Torokhov <dtor@...ightbb.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Turn rdmsr, rdtsc into inline functions, clarify names

On Mon, Aug 07, 2006 at 02:28:45PM +0200, Andi Kleen wrote:
> On Mon, Aug 07, 2006 at 01:09:31PM +0200, Vojtech Pavlik wrote:
> > On Mon, Aug 07, 2006 at 10:48:50AM +0200, Andi Kleen wrote:
> > > On Sun, Aug 06, 2006 at 10:43:44PM -0400, Dmitry Torokhov wrote:
> > > > On Saturday 05 August 2006 23:16, Andi Kleen wrote:
> > > > > This whole thing is broken, e.g. on a preemptive kernel when the
> > > > > code can switch CPUs 
> > > > > 
> > > > 
> > > > Would not preempt_disable fix that?
> > > 
> > > Partially, but you still have other problems. Please just get rid
> > > of it. Why do we have timer code in the kernel if you then chose
> > > not to use it?
> >  
> > The problem is that gettimeofday() is not always fast. 
> 
> When it is not fast that means it is not reliable and then you're
> also not well off using it anyways.

I assume you wanted to say "When gettimeofday() is slow, it means TSC is
not reliable", which I agree with. 

But I need, in the driver, in the no-TSC case use i/o counting, not a
slow but reliable method. And I can't say, from outside the timing
subsystem, whether gettimeofday() is fast or slow.

I assume we could make it work with the monotonic timer instead. 

> Please change that code.
 
I'm not arguing that the code is correct. ;)

-- 
Vojtech Pavlik
Director SuSE Labs
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