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

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Message-ID: <20060807150108.GB85602@muc.de>
Date:	Mon, 7 Aug 2006 17:01:08 +0200
From:	Andi Kleen <ak@....de>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Vojtech Pavlik <vojtech@...e.cz>,
	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 09:32:29AM -0400, Dmitry Torokhov wrote:
> On 8/7/06, Andi Kleen <ak@....de> wrote:
> >On Mon, Aug 07, 2006 at 02:48:55PM +0200, Vojtech Pavlik wrote:
> >> 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.
> >
> >Hmm if that is the only obstacle I can export a "slow gettimeofday" flag.
> >
> >However it would be some work to implement it for all architectures.
> >
> 
> Hmm, would it be easier to export "fast gettimeofday" and assume that
> we have slow gettimeofday by default (so gameport will fall back on io
> counting)?

I would expect fast gettimeofday to be more common than slow.

-Andi
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