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?
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.
David Lang
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.
David Lang
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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