linux-kernel - Re: [PATCH] Remove CONFIG_PM altogether, enable power management all the time

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Date:	Tue, 8 Feb 2011 15:35:29 -0800
From:	Frank Rowand <frank.rowand@...sony.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Len Brown <len.brown@...el.com>,
	Alan Stern <stern@...land.harvard.edu>,
	<linux-pm@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	<linux-embedded@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Remove CONFIG_PM altogether, enable power management
 all the time

On 02/08/11 04:21, Ingo Molnar wrote:

< snip >

> Also, i've Cc:-ed Linus, to check whether the idea to make power management a 
> permanent, core portion of Linux has any obvious downsides we missed.
> 
> Rafael, could you do a defconfig-ish x86 build with and without CONFIG_PM, and post 
> the 'size vmlinux' comparison - so that we can see the size difference? We make some 
> things CONFIG_EXPERT configurable just to enable folks who *really* want to cut down 
> on kernel size to configure it out.

For 2.6.38-rc4, x86_64, CONFIG_NR_CPUS=4:

size vmlinux
   text     data       bss       dec      hex  filename

6553910  3555020   9994240  20103170  132c002  vmlinux    with    CONFIG_PM
6512652  3553116   9994240  20060008  1321768  vmlinux    without CONFIG_PM

  41258     1904         0     43162                      delta


That is big enough for me to care.

Turning on CONFIG_PM also forces a few other options on:

 295a296
 > CONFIG_XEN_SAVE_RESTORE=y
 422c423,431
 < # CONFIG_PM is not set
 ---
 > CONFIG_PM=y
 > # CONFIG_PM_DEBUG is not set
 > CONFIG_PM_SLEEP_SMP=y
 > CONFIG_PM_SLEEP=y
 > # CONFIG_SUSPEND is not set
 > # CONFIG_HIBERNATION is not set
 > # CONFIG_PM_RUNTIME is not set
 > CONFIG_PM_OPS=y
 > # CONFIG_ACPI is not set
 451,454c460
 < CONFIG_CPU_IDLE=y
 < CONFIG_CPU_IDLE_GOV_LADDER=y
 < CONFIG_CPU_IDLE_GOV_MENU=y
 < # CONFIG_INTEL_IDLE is not set
 ---
 > # CONFIG_CPU_IDLE is not set

> 
> Note that those usecases, even if they want a super-small kernel, might not care 
> about PM at all while they care about size: small boot kernels in ROMs, or simple 
> devices where CPU-idling implies deep low power mode, etc.
> 
> So the vmlinux size comparisons would be needed really. If it's 5k nobody will care. 
> If it's 50k-100k that's borderline. In the other side of the scale we have the 1500+
> #ifdef CONFIG_PM lines strewn around the kernel source, and the frequent !PM build
> breakages.
> 
> 	Ingo

-Frank

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