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Subject[RFC/RFT patch 0/7] timekeeping: Unify clock MONOTONIC and clock BOOTTIME
While working through the melted spectrum induced backlog I found that last
years discussion about unifying clock MONOTONIC and clock BOOTTIME has died
out and obviously nobody had time to do testing on that half baken RFC patch:

https://lkml.kernel.org/r/alpine.DEB.2.20.1711180123360.2186@nanos

So I sat down and revisited it a bit more carefully than last time. The
following series is the result of this work. The main differences are:

1) Provide CLOCK_MONOTONIC_ACTIVE which has the current CLOCK_MONOTONIC
behaviour, i.e. it's monotonic time since boot minus the time spent in
suspend.

The reason why I introduced it is that currently it's possible for user
space to determine the time spent in suspend by subtracting clock
monotonic and clock boot time time stamps. When CLOCK_MONOTONIC behaves
like CLOCK_BOOTTIME then this is not longer possible.

As a side effect when CLOCK_MONOTONIC_ACTIVE is supported by a kernel
then this is also an indicator that CLOCK_MONOTONIC and CLOCK_BOOTTIME
are identical. So it's possible to determine this w/o playing games
with kernel versions etc. Older kernels simply return -EiNVAL if
CLOCK_MONOTONIC_ACTIVE is requested in clock_gettime().

2) Fixed a few places which I missed last time, which means also that my
warning in the original changelog was justified.

3) Consolidated the core users to get rid of the seperate implementations
for the two clocks

Note, there are user space visible side effects. The difference between
CLOCK_MONOTONIC and CLOCK_BOOTTIME is well documented and it's unclear
whether applications rely on it or not.

This really needs lot of testing, documentation updates and more input from
userspace folks to make a final decision.

Thanks,

tglx

---

Documentation/trace/ftrace.txt | 14 +-----
drivers/input/evdev.c | 7 ---
include/linux/hrtimer.h | 2
include/linux/timekeeper_internal.h | 2
include/linux/timekeeping.h | 37 +++++------------
include/uapi/linux/time.h | 1
kernel/time/hrtimer.c | 16 -------
kernel/time/posix-stubs.c | 2
kernel/time/posix-timers.c | 26 ++++--------
kernel/time/tick-common.c | 15 ++++++
kernel/time/tick-internal.h | 6 ++
kernel/time/tick-sched.c | 9 ++++
kernel/time/timekeeping.c | 78 ++++++++++++++++++------------------
kernel/time/timekeeping.h | 1
kernel/trace/trace.c | 2
15 files changed, 104 insertions(+), 114 deletions(-)











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