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    SubjectRe: [RFCv4] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes
    On Thu, 10 Mar 2011, Kay Sievers wrote:

    > On Thu, Mar 10, 2011 at 01:25, Andrew Morton <akpm@linux-foundation.org> wrote:
    > > On Wed,  9 Mar 2011 16:36:51 +0200
    > > Alexander Shishkin <virtuoso@slind.org> wrote:
    > >
    > >> Changes since v3:
    > >>  - changed timerfd_settime() semantics (see below)
    > >> Changes since v2:
    > >>  - replaced sysfs interface with a syscall
    > >>  - added sysctl/procfs handle to set a limit to the number of users
    > >>  - fixed issues pointed out by Greg.
    > >> Changes since v1:
    > >>  - updated against 2.6.36-rc1,
    > >>  - added notification/filtering options,
    > >>  - added Documentation/ABI/sysfs-kernel-time-notify interface description.
    >
    > > It would be helpful to know if the identified users of this feature
    > > actually find it useful and adequate.  I guess the most common
    > > application is the 1,001 desktop clock widgets.  Do you have any
    > > feedback from any of the owners of those?
    >
    > We want it for systemd, to provide cron-like functionality but without
    > the need to stupidly wake up every minute and check the system time
    > for possible jumps.
    >
    > It also sounds useful for a generic resume (after system suspend)
    > notification for applications, which isn't really possible today.

    Note, that we have CLOCK_BOOTTIME pending for .39 which aims at the
    same problem. It's basically CLOCK_MONOTONIC adjusted by the time we
    were in suspend. So while CLOCK_MONOTONIC timers are not aware of the
    time spent in suspend CLOCK_BOOTTIME timers are. The reason for
    implementing CLOCK_BOOTTIME was basically the same problem.

    Thanks,

    tglx
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