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

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Oct 16, 2025 at 05:57:36PM +0900, Sergey Senozhatsky wrote:
> On (25/10/16 10:55), Greg KH wrote:
> > 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 :(
> 
> Oh,
> Greg, do you want me to resend or can you just add SoB?
> 

No one can add a signed-off-by for someone else, please go read the
document for exactly what that is attesting.

I've queued up a backport I did with a cc: to you on it already, that
should be identical to yours, right?

thanks,

greg k-h