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From: "Rafael J. Wysocki" <>
To: Len Brown <>
Cc: "Rafael J. Wysocki" <>,
	Linux PM <>,
	Peter Zijlstra <>,
	Daniel Lezcano <>,
	Doug Smythies <>,
	LKML <>
Subject: Re: [PATCH] cpuidle: Consolidate disabled state checks
Date: Mon, 18 Nov 2019 10:22:05 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, Nov 18, 2019 at 5:46 AM Len Brown <> wrote:
> On Mon, Nov 4, 2019 at 6:16 AM Rafael J. Wysocki <> wrote:
> >
> > From: Rafael J. Wysocki <>
> >
> > There are two reasons why CPU idle states may be disabled: either
> > because the driver has disabled them or because they have been
> > disabled by user space via sysfs.
> >
> > In the former case, the state's "disabled" flag is set once during
> > the initialization of the driver and it is never cleared later (it
> > is read-only effectively).
> for x86 (intel_idle and acpi_idle), no states with disabled=1 are  registered
> with cpuidle.  Instead, intel_idle (currently) skips them in the loop
> that registers states.
> (and acpi_idle never touches the disabled field)
> And so for x86, governors checking for drv->states[i].disabled is a NOP,
> and the condition described by CPUIDLE_STATE_DISABLED_BY_DRIVER
> does not (yet) exist.


> Looking at the ARM code, it seems that cpuidle-imx6q.c and cpuidle-tegra20.c
> reach into the cpuidle states at run time and toggle the
> drv->states[i].disabled.

I might have overlooked that, let me check.

> It seems that this patch takes the initial value of
> drv->states->disabled, and sets the (per cpu)
> usage.disable=..BY_DRIVER,
> but that subsequent run-time toggles in drv->states[i]disabled by
> these drivers would be missed,
> because you're removed the run-time checking of drv->states->disabled?

If it is updated at run time, then yes, the updates will be missed, so
thanks for pointing that out.

> Finally, I'd like to change intel_idle so that it *can* register a
> state that is disabled, by default.
> If I change the driver to NOT skip registering disabled states, and
> the cpuidle copy has cpuidle_state.disabled=1,
> then the state is indeed, unused at run-time.  But as you said,
> it is effectively read-only, and is not indicated in sysfs, and can
> not be changed via sysfs.
> One way to do this is to do what you do here and initialize
> usage.disabled to drv->state.disabled. (not distinguishing between
> That way the user could later over-ride what a driver set, by clearing
> the disabled attribute.
> However, the ARM drivers, at least, seem to want to reserve the right
> to set and clear the drv->state.disabled,
> and to have them continue to have that right, we have to continue
> checking that field at run-time.

Alternatively, the drivers in question can be changed to update the
disable field in state_usage instead (maybe under a lock to prevent
them from racing with user space).

> And giving drivers the opportunity to do that disabling driver-wide,
> instead of per-cpu (usage) wide,
> seems to be something we may want to keep.

So it looks like you want me to revert this patch which is something
that I really don't want to do, because of the extra checks all over
the place which are simply pointless in the majority of cases.


  reply	other threads:[~2019-11-18  9:22 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04 11:16 Rafael J. Wysocki
2019-11-04 11:52 ` Peter Zijlstra
2019-11-18  4:45 ` Len Brown
2019-11-18  9:22   ` Rafael J. Wysocki [this message]
2019-11-18 11:26     ` Rafael J. Wysocki
2019-11-18 23:04       ` [RFC][PATCH 0/2] cpuidle: Allow states to be disabled by default (was: Re: [PATCH] cpuidle: Consolidate disabled state checks) Rafael J. Wysocki
2019-11-18 23:07         ` [RFC][PATCH 1/2] cpuidle: Drop disabled field from struct cpuidle_state Rafael J. Wysocki
2019-11-18 23:09         ` [RFC][PATCH 2/2] cpuidle: Allow idle states to be disabled by default Rafael J. Wysocki

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