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Date: Mon, 24 Jun 2002 15:46:20 +0300
From: Matti Aarnio <matti.aarnio@zmailer.org>
To: "Salvatore D'Angelo" <dangelo.sasaman@tiscalinet.it>
Cc: Chris McDonald <chris@cs.uwa.edu.au>, linux-kernel@vger.kernel.org
Subject: Re: gettimeofday problem
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References: <3D16DE83.3060409@tiscalinet.it> <200206240934.g5O9YL524660@budgie.cs.uwa.edu.au> <3D16F252.90309@tiscalinet.it>
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On Mon, Jun 24, 2002 at 12:20:02PM +0200, Salvatore D'Angelo wrote:
> In this piece of code I convert seconds and microseconds in 
> milliseconds. I think the problem is not in my code, in fact I wrote the 
> following piece of code in Java, and it does not work too. In the for 
> loop the 90% of times b > a while for 10% of times not.
> 
...
>                     long a = System.currentTimeMillis();
>                     long b = System.currentTimeMillis();
>                     if (a > b) {
>                          System.out.println("Wrong!!!!!!!!!!!!!");
>                     }


   So in 10% of the cases, two successive calls yield time
   rolling BACK ?

   I used  gettimeofday()  call, and compared the original data
   from the code.

   At a modern uniprocessor machine I never get anything except
   monotonously increasing time (TSC is used in betwen timer ticks
   to supply time increase.)   At a dual processor machine, on
   occasion I do get SAME value twice.   I have never seen time
   rolling backwards.

   Uh..  correction:  216199245  0:-1  -- it did step backwards,
   but only once within about 216 million gettimeofday() calls.
   (I am running 2.4.19-pre8smp at the test box.)

/Matti Aarnio
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