large, spurious[?] TSC skews on AMD 760MPX boards

From: Monty (xiphmont_at_xiph.org)
Date: 07/21/04

  • Next message: Andrew Morton: "Re: [PATCH] Delete cryptoloop" 
    Date:	Wed, 21 Jul 2004 16:40:50 -0400
To: linux-kernel@vger.kernel.org

    [Please keep me in the CC: I apologize for the lack of netiquette in
    not subbing to the list but I have enough trouble keeping up with the
    deluge of user support on my own lists ;-]

    Hello folks,

    short background:

    Ever since getting my first dual Athlon, the system timer was 'not
    quite right' when running at stock speed. Selects, alarms, etc, had a
    strange way of firing fractions of a second or several seconds 'too
    late'. I discovered that overclocking by about 10% made the problem
    magically go away. I've never been entirely comfortable doing that,
    but three dual athlons later (all 760MPX-B2 based boards of different
    makes), it was always the only way to make the problem disappear and I
    didn't think more about it.

    Now that I'm on #3, it is not stable at the overclock I need to make
    the system timer problem disappear, so I finally started hunting for
    the cause. Whenever I run the system stock, I see:

    Jul 20 21:48:26 Snotfish kernel: checking TSC synchronization across CPUs:
    Jul 20 21:48:26 Snotfish kernel: BIOS BUG: CPU#0 improperly initialized, has 6282588 usecs TSC skew! FIXED.
    Jul 20 21:48:26 Snotfish kernel: BIOS BUG: CPU#1 improperly initialized, has -6282588 usecs TSC skew! FIXED.

    When the system is running 'properly', that is to say, overclocked:

    Jul 21 22:08:01 Snotfish kernel: checking TSC synchronization across CPUs: passed.

    This behavior is reproducable on all three of my 760MPX systems (One
    Gigabyte GA-7DPXDW-P, and two MSI K7D Master-L). The amount of the
    reported skew varies in the stock case, but it's always large. Note
    that once in a blue moon, the system will come up with no TSC skew at
    stock timings, and the system timer issues seem to disappear.

    What is the proper route to go about debugging this problem, as I have
    it bottled up here in a reproducability cage?

    I'm attaching the syslog from a 'bad' and a 'good' boot (the good boot
    manufactured from a multiplier/FSB combo that AMD would not approve
    of) as well as /proc/cpu info from this 'good' boot.

    (BTW, these are true and correct Athlon MPs; no cheapo XP-modding
    going on here. Also, all motherboards in question are running most
    recent BIOSes and officially support the CPUs they're using. The K7Ds
    are using MP2400s, the Gigabyte is running MP2800s)

    Thanks,
    Monty

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