Messages in this thread | | | Date | Wed, 23 Mar 2011 14:52:37 +0530 | From | Trinabh Gupta <> | Subject | Re: [RFC PATCH V4 2/5] cpuidle: list based cpuidle driver registration and selection |
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Hi Len,
The goal of the patch series is to remove exported pm_idle function pointer (see http://lkml.org/lkml/2009/8/28/43 and http://lkml.org/lkml/2009/8/28/50 for problems related to pm_idle). The first patch in the series removes pm_idle for x86 and we now directly call cpuidle_idle_call as suggested by Arjan (https://lkml.org/lkml/2010/10/19/453).
But we also have to replace the functionality provided by pm_idle, i.e. call default_idle for platforms where no better idle routine exists, call mwait for pre-nehalem platforms, use intel_idle or acpi_idle for nehalem architectures etc. To manage all this we need a registration mechanism which is conveniently provided by cpuidle.
In theory I agree that we can maybe do without list based registration i.e probe and pick the best for the platform, but things may become less predictable and difficult to manage as we have more and more platforms and drivers. By directly calling into cpuidle, we already have arch default other than intel_idle and acpi_idle. Then APM and xen (though it uses default_idle) also have their own idle routines. List based management and selection based on priority would provide a cleaner solution.
Thanks, -Trinabh
On 03/23/2011 08:29 AM, Len Brown wrote: > the original cpuidle prototype supported multiple driver registration, > but no production use for it could be imagined, and so it was deleted. > > Subsequently on x86, we added intel_idle to replace acpi_idle > and a typical kernel will have them both built in. > We still don't allow mutliple registrations, we just arrange > affairs such that the preferred intel_idle probes before > the backup, acpi_idle. If intel_idle recognizes the platform, > its probe succeeds, else acpi_idle gets a go. > If there is a problem with intel_idle, or a comparison needs to be made, > a bootparam is available to tell intel_idle not to probe. > > This mechanism takes approximately 10 lines of code -- the bootparam > to disable the preferred driver. > > What is the benefit of all the code to support the feature of run-time > multiple driver registration and switching? > > thanks, > Len Brown, Intel Open Source Technology Center > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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