linux-kernel - Re: [PATCH] cpuidle:powernv: Make the snooze timeout dynamic.

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Message-Id: <20180605084529.GA5656@in.ibm.com>
Date:   Tue, 5 Jun 2018 14:15:30 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpuidle:powernv: Make the snooze timeout dynamic.

Hello Michael,

On Mon, Jun 04, 2018 at 09:27:40PM +1000, Michael Ellerman wrote:
> "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> writes:
> 
> > From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> >
> > The commit 78eaa10f027c ("cpuidle: powernv/pseries: Auto-promotion of
> > snooze to deeper idle state") introduced a timeout for the snooze idle
> > state so that it could be eventually be promoted to a deeper idle
> > state. The snooze timeout value is static and set to the target
> > residency of the next idle state, which would train the cpuidle
> > governor to pick the next idle state eventually.
> >
> > The unfortunate side-effect of this is that if the next idle state(s)
> > is disabled, the CPU will forever remain in snooze, despite the fact
> > that the system is completely idle, and other deeper idle states are
> > available.
> 
> That sounds like a bug, I'll add?
>

Yes, this is a bug-fix for a customer scenario which we encountered
recently.

> Fixes: 78eaa10f027c ("cpuidle: powernv/pseries: Auto-promotion of snooze to deeper idle state")
> Cc: stable@...r.kernel.org # v4.2+

This patch applies cleanly from v4.13 onwards. Prior to that there are
some (minor) conflicts.

Should I spin a version separately for the prior stable versions ?

> 
> cheers
>