cpuidle: governors: menu: Avoid using invalid recent intervals data
authorRafael J. Wysocki <rafael.j.wysocki@intel.com>
Mon, 11 Aug 2025 15:03:11 +0000 (17:03 +0200)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Mon, 11 Aug 2025 19:46:14 +0000 (21:46 +0200)
commitfa3fa55de0d6177fdcaf6fc254f13cc8f33c3eed
treedce428a555868f0e83ad8d5489a8859bca106386
parente91a158b694d7f4bd937763dde79ed0afa472d8a
cpuidle: governors: menu: Avoid using invalid recent intervals data

Marc has reported that commit 85975daeaa4d ("cpuidle: menu: Avoid
discarding useful information") caused the number of wakeup interrupts
to increase on an idle system [1], which was not expected to happen
after merely allowing shallower idle states to be selected by the
governor in some cases.

However, on the system in question, all of the idle states deeper than
WFI are rejected by the driver due to a firmware issue [2].  This causes
the governor to only consider the recent interval duriation data
corresponding to attempts to enter WFI that are successful and the
recent invervals table is filled with values lower than the scheduler
tick period.  Consequently, the governor predicts an idle duration
below the scheduler tick period length and avoids stopping the tick
more often which leads to the observed symptom.

Address it by modifying the governor to update the recent intervals
table also when entering the previously selected idle state fails, so
it knows that the short idle intervals might have been the minority
had the selected idle states been actually entered every time.

Fixes: 85975daeaa4d ("cpuidle: menu: Avoid discarding useful information")
Link: https://lore.kernel.org/linux-pm/86o6sv6n94.wl-maz@kernel.org/
Link: https://lore.kernel.org/linux-pm/7ffcb716-9a1b-48c2-aaa4-469d0df7c792@arm.com/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/2793874.mvXUDI8C0e@rafael.j.wysocki
drivers/cpuidle/governors/menu.c