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Date: Wed, 13 Jun 2012 14:44:55 +0200 From: Jean Pihet <jean.pihet@...oldbits.com> To: Daniel Lezcano <daniel.lezcano@...aro.org> Cc: Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>, linux-acpi@...r.kernel.org, linux-pm@...ts.linux-foundation.org, linaro-dev@...ts.linaro.org, linux-kernel@...r.kernel.org, Kevin Hilman <khilman@...com> Subject: Re: [linux-pm] [RFC 1/4] cpuidle: define the enter function in the driver structure Hi Daniel, On Fri, Jun 8, 2012 at 11:34 PM, Daniel Lezcano <daniel.lezcano@...aro.org> wrote: > On 06/08/2012 07:33 PM, Deepthi Dharwar wrote: >> Hi Daniel, > > Hi Deepthi, > >> On 06/08/2012 09:32 PM, Daniel Lezcano wrote: >> >>> We have the state index passed as parameter to the 'enter' function. >>> Most of the drivers assign their 'enter' functions several times in >>> the cpuidle_state structure, as we have the index, we can delegate >>> to the driver to handle their own callback array. >>> >>> That will have the benefit of removing multiple lines of code in the >>> different drivers. >>> >>> In order to smoothly modify the driver, the 'enter' function are in >>> the driver structure and in the cpuidle state structure. That will >>> let the time to modify the different drivers one by one. >>> So the 'cpuidle_enter' function checks if the 'enter' callback is >>> assigned in the driver structure and use it, otherwise it invokes >>> the 'enter' assigned to the cpuidle_state. >> >> >> Currently, the backend driver initializes >> all the cpuidle states supported on the platform, >> and each state can have its own enter routine >> which can be unique This is a clean approach. > > Yes, I perfectly understood the purpose of this field but as clean it is > it does not make sense as it is not used in this way. If it is supposed > to be done in the way you are describing here, we should have the same > number of states and enter functions. Here it is how it is used: > > -------------------------------------------------- > | Arch | nr states | nr enter function | > -------------------------------------------------- > | x86 (nehalem) | 3 | 1 | > -------------------------------------------------- > | x86 (snb) | 4 | 1 | > -------------------------------------------------- > | x86 (atom) | 4 | 1 | > -------------------------------------------------- > | ARM tegra | 1 | 1 | > -------------------------------------------------- > | ARM omap3 | 7 | 2 | > -------------------------------------------------- > | ARM omap4 | 3 | 1 | > -------------------------------------------------- > | ARM ux500 | 2 | 1 | > -------------------------------------------------- > | ARM shmobile | 1 | 1 | > -------------------------------------------------- > | ARM davinci | 2 | 1 | > -------------------------------------------------- > | ARM at91 | 2 | 1 | > -------------------------------------------------- > | ARM s3c64xx | 1 | 1 | > -------------------------------------------------- > | ARM exynos | 2 | 1 | > -------------------------------------------------- > | ARM kirkwood | 2 | 1 | > -------------------------------------------------- > | SH | 3 | 1 | > -------------------------------------------------- > | PPC | 2 | 2 | > -------------------------------------------------- > | | | | > | TOTAL | 39 | 17 | > | | | | > -------------------------------------------------- > > > As you can see most of the enter functions are only used as one. > The Omap3 cpuidle driver enter function for C2 calls the enter function > of C1. Other arch, already use a table of callbacks or the index. There is a plan to remove the extra enter function as part of an optimization, cf. [1]. The fix is planned to reach the 3.6 mainline kernel via Kevin's tree [2]. [1] http://marc.info/?l=linux-omap&m=133856365818099&w=2 [2] http://git.kernel.org/?p=linux/kernel/git/khilman/linux-omap-pm.git;a=shortlog;h=refs/heads/for_3.6/pm/performance The result is that there will be only one enter function for OMAP3. Regards, Jean >> By moving the enter routine into the driver, >> we are enforcing in having only one enter state. >> There is unnecessary overhead involved >> in calling a wrapper routine just to >> index into the right idle state routine >> for many platforms at runtime. > > I don't agree. For the sake of encapsulated code, we duplicate n-times a > field and that is not used in this way. It is quite easy to have in the > driver specific code a common enter function to ventilate to the right > routine without adding extra overhead and let the common code use a > single enter routine (which is already the case today). > > > _______________________________________________ > linux-pm mailing list > linux-pm@...ts.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/linux-pm -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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