tree 695c2c728bfbfe638060dd4fdf86457acd6bf8d3
parent 5ed9a80571ede30d4cb7967227bff996c9cecb9e
author Christopher Tate <ctate@google.com> 1297201141 -0800
committer Christopher Tate <ctate@google.com> 1297213186 -0800

Align inexact alarms in both time bases; don't pull to wall time

The previous implementation failed to properly distinguish between
trigger times in the RTC vs the ELAPSED time bases.  The pernicious
result of this was that sometimes it would decide to align RTC
alarms based on, say, 0 rather than on the real current time.
This would pull the recurrence into wall-clock alignment, with
serious side effects: in particular, periodic tasks that would hit
external network resources would, because *all* devices would be
pulled into wall-clock alignment, wind up inducing heavy QPS
spikes on the backends.

The new implementation works completely differently.  The basic
goal is the same: try to align inexact alarms to "the same" time,
avoiding extra wakeups / radio spinups / etc.  The way this is done
is to divide the timeline into 15-minute quanta, and drift the start
time of every inexact alarm onto one of these 15-minute quantum
boundaries.  The skew between the RTC and ELAPSED time bases is
taken into effect; RTC alarms are no longer pulled into wall clock
alignment.

Fixes bug 3388961

Change-Id: I2a0460e1f5d0e4036f3402f332b642b557b2fc20