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    SubjectRe: Linux 2.2.18: /proc/apm slows system time (was: Linux 2.2.19pre3)
    On Thu, Dec 28, 2000 at 02:53:37PM +0100, Matthias Andree wrote:
    > Forget this all.
    >
    > I found the problem trigger, it's reading from /proc/apm, for a reason I
    > cannot currently see.
    >
    > Current config, as far as it's APM-related:
    > CONFIG_APM=y
    > # CONFIG_APM_IGNORE_USER_SUSPEND is not set
    > # CONFIG_APM_DO_ENABLE is not set
    > # CONFIG_APM_CPU_IDLE is not set
    > # CONFIG_APM_DISPLAY_BLANK is not set
    > CONFIG_APM_RTC_IS_GMT=y
    > CONFIG_APM_ALLOW_INTS=y
    > # CONFIG_APM_REAL_MODE_POWER_OFF is not set
    > # CONFIG_TOSHIBA is not set
    >
    > I had found out that my clock was slow while dnetc was running. I had a
    > dummy loader that just did while(1) {} which did not slow my clock. Now, I
    > straced that dnetc beast and found out that it reads /proc/apm quite
    > often.

    I got the same problem while running the GNOME battery_applet, which
    checks /proc/apm every 2 seconds.

    > I can have my clock almost halt with this one:
    >
    > while cat /proc/apm ; do : ; done
    >
    > If I leave this running for 15 s, my system time drifts back 11½ s.

    Same over here on an Asus M8300 notebook (Celeron 500, 128MB, Intel
    440MX chipset). Output from /proc/apm:

    1.14 1.2 0x03 0x01 0x03 0x09 100% -1 ?

    I also enabled CONFIG_APM_ALLOW_INTS to see if it makes any difference,
    but apparently it doesn't.

    However, reading from /proc/apm also triggers other weird problems:

    - Sound hickups: mp3 output starts to sound "scratchy". problem
    disappears after restarting mp3 player or after a couple of reads
    from /proc/apm. This is with mpg123, xmms, and madplay.
    - USB drop outs, especially for bulk devices like scanners or USB audio
    devices. For sound it usually takes a second or so to restart.
    - Received characters dropped on serial line. I thought my serial port
    was broken, because a 16550 is supposed to have a receive buffer.

    All these problems went away when I removed the GNOME battery_applet.

    I got the same problems with my previous notebook (Asus P6300, PII 266,
    112MB, Intel BX/ZX chipset). It might be a BIOS problem, because both
    notebooks use a Phoenix BIOS. OTOH, I can create the same problems with
    USB on my desktop (Asus P5A motherboard, K6 333, 160MB, Ali 1541
    chipset, Award BIOS) when I run the GNOME battery_applet. So is this an
    Asus problem, or a general APM problem?


    Erik

    --
    J.A.K. (Erik) Mouw, Information and Communication Theory Group, Department
    of Electrical Engineering, Faculty of Information Technology and Systems,
    Delft University of Technology, PO BOX 5031, 2600 GA Delft, The Netherlands
    Phone: +31-15-2783635 Fax: +31-15-2781843 Email: J.A.K.Mouw@its.tudelft.nl
    WWW: http://www-ict.its.tudelft.nl/~erik/
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