time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64()

The internal clocksteering done for fine-grained error
correction uses a logarithmic approximation, so any time
adjtimex() adjusts the clock steering, timekeeping_freqadjust()
quickly approximates the correct clock frequency over a series
of ticks.

Unfortunately, the logic in timekeeping_freqadjust(), introduced
in commit:

  dc491596f639 ("timekeeping: Rework frequency adjustments to work better w/ nohz")

used the abs() function with a s64 error value to calculate the
size of the approximated adjustment to be made.

Per include/linux/kernel.h:

  "abs() should not be used for 64-bit types (s64, u64, long long) - use abs64()".

Thus on 32-bit platforms, this resulted in the clocksteering to
take a quite dampended random walk trying to converge on the
proper frequency, which caused the adjustments to be made much
slower then intended (most easily observed when large
adjustments are made).

This patch fixes the issue by using abs64() instead.

Reported-by: Nuno Gonçalves <[email protected]>
Tested-by: Nuno Goncalves <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Cc: <[email protected]> # v3.17+
Cc: Linus Torvalds <[email protected]>
Cc: Miroslav Lichvar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: Richard Cochran <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions