From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: Re: [GIT PATCH] ACPI patches for 2.6.23-rc1 Date: Wed, 25 Jul 2007 18:51:22 -0400 Message-ID: <200707251851.22777.lenb@kernel.org> References: <200707251238.50218.lenb@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:54644 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756293AbXGYWv2 (ORCPT ); Wed, 25 Jul 2007 18:51:28 -0400 In-Reply-To: Content-Disposition: inline Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Linus Torvalds Cc: Andrew Morton , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org 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. 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. 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