linux-kernel - Re: CONFIG_SUSPEND? (was: Re: [GIT PATCH] ACPI patches for 2.6.23-rc1)

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Date:	Sat, 28 Jul 2007 20:29:02 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Len Brown <lenb@...nel.org>, david@...g.hm,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>
Subject: Re: CONFIG_SUSPEND? (was: Re: [GIT PATCH] ACPI patches for 2.6.23-rc1)

On Saturday, 28 July 2007 18:55, Linus Torvalds wrote:
> 
> On Sat, 28 Jul 2007, Linus Torvalds wrote:
> > 
> > And it's the *top*level* code that selects HOTPLUG_CPU. Through 
> > SUSPEND_SMP (which will select HOTPLUG_CPU) and SOFTWARE_SUSPEND.
> 
> In other words, the problem seems to be that 
> 
> 	kernel/power/main.c:
> 		suspend_devices_and_enter()
> 
> does the proper "disable/enable_nonboot_cpus()", but it does so without 
> having enabled CPU hotplug.
> 
> And you seem to think that it's ACPI that should enable the hotplug, even 
> though the code that actually needs it is _outside_ ACPI. And I think 
> that's wrong, and that this is a bug.
> 
> So I think the real issue is that we allow that 
> "suspend_devices_and_enter()" code to be compiled without HOTPLUG_CPU in 
> the first place. It's not supposed to work that way.
> 
> Of course, it may well be that other architectures can happily suspend 
> even with multiple CPU's active, which may be the cause of this mess. But 
> I really think it shouldn't be ACPI that has to select the CPU hotplug, 
> since it's not ACPI that _uses_ it in the first place.
> 
> Rafael: making a config option for STR (the same way we have a config 
> option for hibernate), and just not allowing it on SMP without HOTPLUG_CPU 
> seems to be the right thing. Len is right in that we do insane things 
> right now (trying to STR with multiple CPU's still active), and I just 
> don't think he's the one that should work around it!

Well, I agree and that's why I asked. :-)

OK, I'll prepare a patch to introduce CONFIG_SUSPEND, but that will require
quite a bit of (compilation) testing on different architectures.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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