Messages in this thread Patch in this message | | | Date | Sun, 5 Oct 2008 17:20:25 +0200 | From | Ingo Molnar <> | Subject | Re: <PING> Re: [patch x86/core] x86: allow number of additional hotplug CPUs to be set at compile time |
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* Thomas Gleixner <tglx@linutronix.de> wrote:
> On Sun, 5 Oct 2008, Ingo Molnar wrote: > > * Chuck Ebbert <cebbert@redhat.com> wrote: > > > > > Yes, it works and I don't see how it could cause any problems. > > > > > > Ingo, can we get this in 2.6.27? You can drop my original patch. > > > > > > Tested-by: Chuck Ebbert <cebbert@redhat.com> > > > > looks good, applied to tip/x86/core, thanks! > > No, this patch is horrible. > > The correct check is num_present_cpus(). There is no need to make the > weird additional_cpus hackery globally available.
ah, indeed!
applied to tip/x86/core and i've zapped Andi's patch.
> Btw, additional_cpus has interesting properties. Providing a negative > number < -1 on the kernel command line - happened due to a typo - > explodes in early boot, which is not really surprising, but should be > sanity checked.
indeed, and that mess was introduced, interestingly, by this commit, three years ago, by Andi:
| From 420f8f68c9c5148dddf946bebdbc7eacde2172cb Mon Sep 17 00:00:00 2001 | From: Andi Kleen <ak@suse.de> | Date: Sat, 5 Nov 2005 17:25:54 +0100 | Subject: [PATCH] [PATCH] x86_64: New heuristics to find out hotpluggable CPUs.
so to clean up the mess i've removed the additional_cpus= boot parameter and the Kconfig entry as well - see the patch in x86/core below.
thanks Thomas for decoding this ...
and no way can any of this go into v2.6.27: this is fragile code with a lot of historic baggage and the original error is non-fatal to begin with. It can easily be backported to .27.1 if testing shows that it has no other adverse side-effects.
Ingo
------------------> From a3f493ab543d300b3a01ad18bf12f73746ae5c9f Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@elte.hu> Date: Sun, 5 Oct 2008 17:12:36 +0200 Subject: [PATCH] x86: remove additional_cpus configurability
additional_cpus=<x> parameter is dangerous and broken: for example if we boot additional_cpus=-2 on a stock dual-core system it will crash the box on bootup.
So reduce the maze of code a bit by removingthe user-configurability angle.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- arch/x86/Kconfig | 18 ------------------ arch/x86/kernel/smpboot.c | 8 +------- 2 files changed, 1 insertions(+), 25 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 7dff081..e2c060e 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1365,24 +1365,6 @@ config HOTPLUG_CPU Say N if you want to disable CPU hotplug and don't need to suspend. -config HOTPLUG_RESTRICT_TO_BOOTUP_CPUS - def_bool n - prompt "Restrict CPU hotplugging to processors found during boot" if HOTPLUG_CPU - ---help--- - Say no here to use the default, which allows as many CPUs as are marked - "disabled" by ACPI or MPTABLES to be hotplugged after bootup. - - Say yes if you do not want to allow CPUs to be added after booting, for - example if you only need CPU hotplugging enabled for suspend/resume. - - If CPU_HOTPLUG is enabled this value may be overridden at boot time - with the "additional_cpus" kernel parameter. - -config HOTPLUG_ADDITIONAL_CPUS - int - default 0 if !HOTPLUG_CPU || HOTPLUG_RESTRICT_TO_BOOTUP_CPUS - default -1 - config COMPAT_VDSO def_bool y prompt "Compat VDSO support" diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 9ac428a..3868018 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1260,7 +1260,7 @@ void __init native_smp_cpus_done(unsigned int max_cpus) check_nmi_watchdog(); } -static int additional_cpus __initdata = CONFIG_HOTPLUG_ADDITIONAL_CPUS; +static int additional_cpus = -1; /* * cpu_possible_map should be static, it cannot change as cpu's @@ -1333,12 +1333,6 @@ static void remove_siblinginfo(int cpu) cpu_clear(cpu, cpu_sibling_setup_map); } -static __init int setup_additional_cpus(char *s) -{ - return s && get_option(&s, &additional_cpus) ? 0 : -EINVAL; -} -early_param("additional_cpus", setup_additional_cpus); - static void __ref remove_cpu_from_maps(int cpu) { cpu_clear(cpu, cpu_online_map);
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