Date: Thu, 10 Nov 2005 22:04:58 +0100
From: Ingo Molnar <mingo@elte.hu>
To: john stultz <johnstul@us.ibm.com>
Cc: dino@in.ibm.com, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: IO-APIC problem with 2.6.14-rt9
Message-ID: <20051110210458.GA6097@elte.hu>
References: <20051110200226.GA18780@in.ibm.com> <20051110200205.GA4696@elte.hu> <20051110203000.GB16301@in.ibm.com> <1131654575.27168.685.camel@cog.beaverton.ibm.com>
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* john stultz <johnstul@us.ibm.com> wrote:

> > > //#define ARCH_HAS_READ_CURRENT_TIMER  1
> > > 
> > > to:
> > > 
> > > #define ARCH_HAS_READ_CURRENT_TIMER  1
> > > 
> > > ?
> > 
> > It works !!  Thanks Ingo for the immediate response
> 
> Hrm. Could you post the value for BogoMIPS that you're getting now?
> 
> My patches touch the __delay() code, since using the TSC based delay 
> has just as many, if not more, problems as the loop based delay. So I 
> want to be careful that my changes are not further causing problems.
> 
> Ingo, did you commented out ARCH_HAS_READ_CURRENT_TIMER because of 
> problems with the new calibration code?

yes. traces show that the new calibration code results in a bogomips 
value on Athlon64 CPUs that halve the timeout. I.e. udelay(100) now 
takes 50 usecs (!). The calibration code seems to assume the number of 
cycles == number of loops in __delay() - that is not valid. The 
calibration needs to happen based on some real clock, such as the PIT, 
or PIT-driven jiffies.

	Ingo
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