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    SubjectRe: [linux-pm] [PATCH 0/8] Suspend block api (version 6)
    Alan Stern <> writes:

    > On Fri, 14 May 2010, Brian Swetland wrote:
    >> In tickless mode, the time until next timer is a signed int, so the
    >> longest the kernel will ever sleep is ~2 seconds at a go. In
    >> practice, userspace entities often have polling behavior that can
    >> trigger more often than that, and I've observed some kernel periodic
    >> timers (haven't cataloged them recently) that happen more often than
    >> once a second.
    > Paul and Kevin, how does the OMAP implementation handle these
    > difficulties?

    just a minor clarification... these aren't OMAP-specific issues, but
    generic issues to all power-sensitive kernel users.

    The ~2 second limit was fixed by Jon Hunter (TI) and is in mainline
    since 2.6.32[1].

    For other timers, there has been active work (mostly by Intel folks)
    on deferrable timers, coalescing timers, timer slack etc. that has
    greatly reduced the kernel timer impact on wakeups.

    > Also, how does it handle the issue of ill-behaved apps?

    For userspace, apps that have polling behavior or are ill-behaved must
    be found and fixed. Thanks to tools like powertop, this is a farily
    easy task.

    But really, I don't consider the "ill-behaved app" problem to be a
    real-world problem. Both in maemo/meego and Android, if someone
    writes an app that kills battery life, it will get reported as a bug,
    or get bad ratings etc. On these kinds of devices, there is a *stong*
    developer incentive to not write battery sucking apps.


    commit 97813f2fe77804a4464564c75ba8d8826377feea
    Author: Jon Hunter <>
    Date: Tue Aug 18 12:45:11 2009 -0500

    nohz: Allow 32-bit machines to sleep for more than 2.15 seconds

    In the dynamic tick code, "max_delta_ns" (member of the
    "clock_event_device" structure) represents the maximum sleep time
    that can occur between timer events in nanoseconds.

    The variable, "max_delta_ns", is defined as an unsigned long
    which is a 32-bit integer for 32-bit machines and a 64-bit
    integer for 64-bit machines (if -m64 option is used for gcc).
    The value of max_delta_ns is set by calling the function
    "clockevent_delta2ns()" which returns a maximum value of LONG_MAX.
    For a 32-bit machine LONG_MAX is equal to 0x7fffffff and in
    nanoseconds this equates to ~2.15 seconds. Hence, the maximum
    sleep time for a 32-bit machine is ~2.15 seconds, where as for
    a 64-bit machine it will be many years.

    This patch changes the type of max_delta_ns to be "u64" instead of
    "unsigned long" so that this variable is a 64-bit type for both 32-bit
    and 64-bit machines. It also changes the maximum value returned by
    clockevent_delta2ns() to KTIME_MAX. Hence this allows a 32-bit
    machine to sleep for longer than ~2.15 seconds. Please note that this
    patch also changes "min_delta_ns" to be "u64" too and although this is
    unnecessary, it makes the patch simpler as it avoids to fixup all
    callers of clockevent_delta2ns().

    [ tglx: changed "unsigned long long" to u64 as we use this data type
    through out the time code ]

    Signed-off-by: Jon Hunter <>
    Cc: John Stultz <>
    LKML-Reference: <>
    Signed-off-by: Thomas Gleixner <>

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      Last update: 2010-05-17 17:43    [W:0.024 / U:1.628 seconds]
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