[PATCH v2 0/2] alarmtimer: Rework the suspend flow in alarmtimer

From: Pranav Prasad
Date: Thu Feb 08 2024 - 14:56:45 EST


During the driver suspend phase of kernel suspend, alarmtimer's suspend
callback is invoked and it identifies the earliest next wakeup alarm and
programs that into the HW real time clock (RTC). However, there is an
exception to this process. If the next alarm is within the next 2 seconds,
the alarmtimer driver fails to suspend. In this case, a non-trivial amount
of power is spent to freeze and unfreeze all userspace processes and to
suspend and resume a number of devices. In the vast majority of cases, the
imminent alarm that caused the failure was likely already scheduled before
suspend even started. This provides an opportunity to reduce power
consumption if the suspend failure decision is made earlier in the suspend
flow, before the unnecessary extra work is done.

This patch series aims to achieve a kernel suspend flow in which the check
for an imminent alarm is performed early during the suspend prepare phase.

Changes from v1:

- Moved the pm_wakeup_event call to the PM notifier
- Added a check for RTC device in the PM notifier

Pranav Prasad (2):
alarmtimer: Create alarmtimer sysfs to make duration of kernel suspend
check configurable
alarmtimer: Modify alarmtimer suspend callback to check for imminent
alarm using PM notifier

kernel/time/alarmtimer.c | 183 ++++++++++++++++++++++++++++++---------
1 file changed, 143 insertions(+), 40 deletions(-)