Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 18 Nov 2019 12:26:57 +0100 | Subject | Re: [PATCH] cpuidle: Consolidate disabled state checks |
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On Mon, Nov 18, 2019 at 10:22 AM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Mon, Nov 18, 2019 at 5:46 AM Len Brown <lenb@kernel.org> wrote: > > > > On Mon, Nov 4, 2019 at 6:16 AM Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > > > > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > > > 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. > > OK > > > 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 > > DRIVER and USER) > > That way the user could later over-ride what a driver set, by clearing > > the disabled attribute.
I'd rather get rid of the "disabled" field from struct cpuidle_state entirely and introduce a new state flag to indicate the "disabled by default" status.
I also would expose that new flag in a new sysfs attribute of idle states, say "disable_default".
Then, the DISABLED_BY_DRIVER bit would be reserved for driver quirks (as per https://patchwork.kernel.org/patch/11249519/) and the DISABLED_BY_USER one could be used for all of the other purposes.
Cheers, Rafael
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