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From: Len Brown <>
To: "Rafael J. Wysocki" <>
Cc: Linux PM <>,
	Peter Zijlstra <>,
	Daniel Lezcano <>,
	Doug Smythies <>,
	LKML <>
Subject: Re: [PATCH] cpuidle: Consolidate disabled state checks
Date: Sun, 17 Nov 2019 23:45:53 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <2717750.dCEzHT3DVQ@kreacher>

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

It seems that this patch takes the initial value of
drv->states->disabled, and sets the (per cpu)
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?

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.
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.


Len Brown, Intel Open Source Technology Center

  parent reply	other threads:[~2019-11-18  4:46 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 [this message]
2019-11-18  9:22   ` Rafael J. Wysocki
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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