Re: [PATCH 6.1.y] cpuidle: governors: menu: Avoid using invalid recent intervals data

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Oct 14, 2025 at 10:03:00PM +0900, Sergey Senozhatsky wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> 
> [ Upstream commit fa3fa55de0d6177fdcaf6fc254f13cc8f33c3eed ]
> 
> 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/ [1]
> Link: https://lore.kernel.org/linux-pm/7ffcb716-9a1b-48c2-aaa4-469d0df7c792@arm.com/ [2]
> 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
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> (cherry picked from commit 7337a6356dffc93194af24ee31023b3578661a5b)

You forgot to sign off on this :(