linux-kernel - Re: [GIT PATCH] ACPI patches for 2.6.23-rc1

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Message-Id: <200707260026.08183.lenb@kernel.org>
Date:	Thu, 26 Jul 2007 00:26:08 -0400
From:	Len Brown <lenb@...nel.org>
To:	david@...g.hm
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] ACPI patches for 2.6.23-rc1

On Wednesday 25 July 2007 22:20, david@...g.hm wrote:
> On Wed, 25 Jul 2007, Len Brown wrote:
> 
> > On Wednesday 25 July 2007 14:48, Linus Torvalds wrote:
> >
> >> ... ACPI now seems to select CPU hotplug. Why?
> >
> > ACPI=y SMP=y systems require SUSPEND_SMP=y for system sleep support,
> > and that requires HOTPLUG_CPU=y.
> >
> > Note that ACPI=y SMP=n systems do not need it,
> > and thus will not select HOTPLUG_CPU=y
> >
> >> That is just *broken*. Sure, if you select STR or hibernation, we need CPU
> >> hotplug, but just for picking ACPI? Why?
> >
> > My assumption is that if somebody selects CONFIG_ACPI,
> > that 99% of the time, they intend that to include support for
> > the ACPI hooks for system sleep states.
> >
> > Conversely, supporting the 1% of people who don't want it
> > isn't worth messing with the 99% who do, nor is
> > the burden of yet another config option to maintain and
> > #ifdefs in the code.
> 
> so you are saying that you know better then we do what we need?

Feel free to share what you know about the benefits vs. the costs
of maintaining CONFIG_ACPI_SLEEP as a build option.

> some people configure ACPI only becouse their system won't work properly 
> without it. they have no intention of ever doing a STR or hibernate.

I agree.

Further, I expect that 100% - (some people %) = 99%

If you feel that your system has been degraded
because it now includes what used to be excluded under
CONFIG_ACPI_SLEEP=n, please let me know how.

> > On UP, they'd get ACPI system sleep support 100% of the time
> > by default, but on SMP this option had become problematic.
> >
> > We used to have this:
> >
> > if ACPI
> > ...
> > config ACPI_SLEEP
> >        bool "Sleep States"
> >        depends on X86 && (!SMP || SUSPEND_SMP)
> >        depends on PM
> >        default y
> >
> > So the poster-child failure was i386/defconfig itself...
> > It couldn't support suspend to RAM because it didn't include
> > CONFIG_ACPI_SLEEP.  Not trivial for a user to select it
> > when it doesn't even appear on the menu.  It doesn't appear
> > because CONFIG_SUSPEND_SMP isn't enabled, but that doesn't
> > appear either -- because CONFIG_HOTPLUG_CPU isn't selected.
> 
> so have something like
> 
> config ACPI_SLEEP
>          select HOTPLUG_CPU if X86 && SMP
>          select SUSPEND_SMP if X86 && SMP
> 
> instead of makeing it dependant on ACPI.

If more config options where better, then this
would indeed be an improvement over 2.6.22.
But more config options isn't better -- except for "some people":-)

thanks.
-Len

> > Most users don't want that.
> >
> > So today we have this:
> >
> > menuconfig ACPI
> > 	...
> >        select HOTPLUG_CPU if X86 && SMP
> >        select SUSPEND_SMP if X86 && SMP
> >
> > Which I think leads to fewer surprises, and less complicated code.
> > (even though using select itself is fraught with peril:-)
> >
> > thanks,
> > -Len
> >
> > -
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> >
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