Is there a problem in timeval_to_jiffies?

From: Henry Margies (henry.margies_at_gmx.de)
Date: 09/09/04

  • Next message: rom.132: "floppy problem 2.6.9" 
    Date:	Thu, 9 Sep 2004 15:48:28 +0200
To: linux-kernel@vger.kernel.org

    Hallo.

    I'm working on an arm based embedded device running kernel 2.6.9.
    I asked this question also on the arm mailing list, but nobody
    could answer me my questions there, so I will try here :)

    I have some problems with itimers. For example, if I set up a
    timer using a period of 20ms, the system needs 30ms to send the
    signal. I figured out, that it needs always 10ms more than I
    want.

    The problem seems to be located in the timeval_to_jiffies()
    function.

    In function do_setitimer() the following calculation is done:

         i = timeval_to_jiffies(&value->it_interval);

    ... where i is the interval for my timer. The problem is, that
    for it_interval = 0 seconds and 20000 microseconds, i = 3. But
    shouldn't it be 2? It looks like, the problem is somewhere in
    here (timeval_to_jiffies()):

          return (((u64)sec * SEC_CONVERSION) +
                    (((u64)usec * USEC_CONVERSION + USEC_ROUND) >>
                     (USEC_JIFFIE_SC - SEC_JIFFIE_SC))) >>
                            SEC_JIFFIE_SC;

    I don't understand all of the formula in detail. But for me, it
    looks like the problem is in USEC_ROUND.

    Any ideas?

    Thx in advance,
    Henry 

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