From: Len Brown <email@example.com> To: "Rafael J. Wysocki" <firstname.lastname@example.org> Cc: Linux PM <email@example.com>, Peter Zijlstra <firstname.lastname@example.org>, Daniel Lezcano <email@example.com>, Doug Smythies <firstname.lastname@example.org>, LKML <email@example.com> Subject: Re: [PATCH] cpuidle: Consolidate disabled state checks Date: Sun, 17 Nov 2019 23:45:53 -0500 [thread overview] Message-ID: <CAJvTdKn9wuoXkKecZxCJHPZAG7XK_BqAZT5=7k9Mi4zo4SBL0g@mail.gmail.com> (raw) In-Reply-To: <2717750.dCEzHT3DVQ@kreacher> On Mon, Nov 4, 2019 at 6:16 AM Rafael J. Wysocki <firstname.lastname@example.org> wrote: > > From: Rafael J. Wysocki <email@example.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. 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. 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? 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. 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 -- Len Brown, Intel Open Source Technology Center
next prev 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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