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

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Date:	Tue, 8 Feb 2011 13:21:59 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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

* Rafael J. Wysocki <rjw@...k.pl> wrote:

> I'd appreciate it if people could review/test it and drop their comments.
> 
> Thanks,
> Rafael
> 
> ---
>  arch/x86/xen/Kconfig               |    2 +-
>  drivers/acpi/Kconfig               |    1 -
>  drivers/acpi/bus.c                 |    4 +---
>  drivers/acpi/internal.h            |    6 ++++++
>  drivers/acpi/sleep.c               |   13 +++++++++++--
>  drivers/base/power/Makefile        |    3 +--
>  drivers/net/e1000e/netdev.c        |    8 ++++----
>  drivers/net/pch_gbe/pch_gbe_main.c |    2 +-
>  drivers/pci/pci-driver.c           |    4 ++--
>  drivers/scsi/Makefile              |    2 +-
>  drivers/scsi/scsi_priv.h           |    2 +-
>  drivers/scsi/scsi_sysfs.c          |    2 +-
>  drivers/usb/core/hcd-pci.c         |    4 ++--
>  include/acpi/acpi_bus.h            |    2 +-
>  include/linux/pm.h                 |    2 +-
>  kernel/power/Kconfig               |   29 +++--------------------------
>  16 files changed, 37 insertions(+), 49 deletions(-)

Ok, there's some real bang for bucks in this patch, nice! It's a beginning.

Reviewed-by: Ingo Molnar <mingo@...e.hu>

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.

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
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