[patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Natalie.Protasevich]

Current IA32 CPU hotplug code doesn't allow bringing up processors that were not present in the boot configuration. 
To make existing hot plug facility more practical for physical hot plug, possible processors should be encountered 
during boot for potentual hot add/replace/remove. On ES7000, ACPI marks all the sockets that are empty or not assigned
to the partitionas as "disabled". The patch allows arrays/masks with APIC info for disabled processors to be 
initialized. Then the OS can bring up a processor that was inserted in the socked and brought into configuration 
during runtime. 
To test the code, one can boot the system with maxcpu=1 and then bring the rest of the processors up, which was not 
possible so far (only maxcpus number of nodes were created).
The patch also makes proc entry for interrupts dynamically change to only show current onlined processors.

Signed-off-by: Natalie Protasevich  <Natalie.Protasevich@unisys.com>
---

 arch/i386/kernel/acpi/boot.c      |    2 ++
 arch/i386/kernel/irq.c            |    8 ++++----
 arch/i386/kernel/mpparse.c        |    4 ++++
 arch/i386/kernel/smpboot.c        |    3 ++-
 arch/i386/mach-default/topology.c |    4 ++--
 kernel/cpu.c                      |    4 ++++
 6 files changed, 18 insertions(+), 7 deletions(-)

diff -puN arch/i386/kernel/acpi/boot.c~hotcpu-i386 arch/i386/kernel/acpi/boot.c
--- linux-2.6.13-rc6-mm2/arch/i386/kernel/acpi/boot.c~hotcpu-i386	2005-08-31 04:17:20.832038600 -0700
+++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/acpi/boot.c	2005-08-31 04:19:35.259602504 -0700
@@ -255,9 +255,11 @@ acpi_parse_lapic(acpi_table_entry_header
 
 	acpi_table_print_madt_entry(header);
 
+#ifndef CONFIG_HOTPLUG_CPU
 	/* no utility in registering a disabled processor */
 	if (processor->flags.enabled == 0)
 		return 0;
+#endif
 
 	x86_acpiid_to_apicid[processor->acpi_id] = processor->id;
 
diff -puN arch/i386/kernel/mpparse.c~hotcpu-i386 arch/i386/kernel/mpparse.c
--- linux-2.6.13-rc6-mm2/arch/i386/kernel/mpparse.c~hotcpu-i386	2005-08-31 04:17:20.877031760 -0700
+++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/mpparse.c	2005-08-31 04:20:49.297347056 -0700
@@ -125,8 +125,10 @@ static void __init MP_processor_info (st
  	int ver, apicid, cpu, found_bsp = 0;
 	physid_mask_t tmp;
  	
+#ifndef CONFIG_HOTPLUG_CPU
 	if (!(m->mpc_cpuflag & CPU_ENABLED))
 		return;
+#endif
 
 	apicid = mpc_apic_id(m, translation_table[mpc_record]);
 
@@ -190,11 +192,13 @@ static void __init MP_processor_info (st
 		return;
 	}
 
+#ifndef CONFIG_HOTPLUG_CPU
 	if (num_processors >= maxcpus) {
 		printk(KERN_WARNING "WARNING: maxcpus limit of %i reached."
 			" Processor ignored.\n", maxcpus); 
 		return;
 	}
+#endif
 	num_processors++;
 	ver = m->mpc_apicver;
 
diff -puN arch/i386/kernel/smpboot.c~hotcpu-i386 arch/i386/kernel/smpboot.c
--- linux-2.6.13-rc6-mm2/arch/i386/kernel/smpboot.c~hotcpu-i386	2005-08-31 04:17:20.924024616 -0700
+++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/smpboot.c	2005-08-31 04:21:49.474198784 -0700
@@ -1003,9 +1003,10 @@ int __devinit smp_prepare_cpu(int cpu)
 	struct warm_boot_cpu_info info;
 	struct work_struct task;
 	int	apicid, ret;
+	extern u8 bios_cpu_apicid[NR_CPUS];
 
 	lock_cpu_hotplug();
-	apicid = x86_cpu_to_apicid[cpu];
+	apicid = bios_cpu_apicid[cpu];
 	if (apicid == BAD_APICID) {
 		ret = -ENODEV;
 		goto exit;
diff -puN arch/i386/mach-default/topology.c~hotcpu-i386 arch/i386/mach-default/topology.c
--- linux-2.6.13-rc6-mm2/arch/i386/mach-default/topology.c~hotcpu-i386	2005-08-31 04:17:20.957019600 -0700
+++ linux-2.6.13-rc6-mm2-root/arch/i386/mach-default/topology.c	2005-08-31 04:22:13.020619184 -0700
@@ -76,7 +76,7 @@ static int __init topology_init(void)
 	for_each_online_node(i)
 		arch_register_node(i);
 
-	for_each_present_cpu(i)
+	for_each_cpu(i)
 		arch_register_cpu(i);
 	return 0;
 }
@@ -87,7 +87,7 @@ static int __init topology_init(void)
 {
 	int i;
 
-	for_each_present_cpu(i)
+	for_each_cpu(i)
 		arch_register_cpu(i);
 	return 0;
 }
diff -puN kernel/cpu.c~hotcpu-i386 kernel/cpu.c
--- linux-2.6.13-rc6-mm2/kernel/cpu.c~hotcpu-i386	2005-08-31 04:17:21.002012760 -0700
+++ linux-2.6.13-rc6-mm2-root/kernel/cpu.c	2005-08-31 04:23:34.378250944 -0700
@@ -158,7 +158,11 @@ int __devinit cpu_up(unsigned int cpu)
 	if ((ret = down_interruptible(&cpucontrol)) != 0)
 		return ret;
 
+#ifdef CONFIG_HOTPLUG_CPU
+	if (cpu_online(cpu)) {
+#else
 	if (cpu_online(cpu) || !cpu_present(cpu)) {
+#endif
 		ret = -EINVAL;
 		goto out;
 	}
diff -puN arch/i386/kernel/irq.c~hotcpu-i386 arch/i386/kernel/irq.c
--- linux-2.6.13-rc6-mm2/arch/i386/kernel/irq.c~hotcpu-i386	2005-08-31 04:17:21.047005920 -0700
+++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/irq.c	2005-08-31 04:25:21.761926144 -0700
@@ -248,7 +248,7 @@ int show_interrupts(struct seq_file *p, 
 
 	if (i == 0) {
 		seq_printf(p, "           ");
-		for_each_cpu(j)
+		for_each_online_cpu(j)
 			seq_printf(p, "CPU%d       ",j);
 		seq_putc(p, '\n');
 	}
@@ -262,7 +262,7 @@ int show_interrupts(struct seq_file *p, 
 #ifndef CONFIG_SMP
 		seq_printf(p, "%10u ", kstat_irqs(i));
 #else
-		for_each_cpu(j)
+		for_each_online_cpu(j)
 			seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
 #endif
 		seq_printf(p, " %14s", irq_desc[i].handler->typename);
@@ -276,12 +276,12 @@ skip:
 		spin_unlock_irqrestore(&irq_desc[i].lock, flags);
 	} else if (i == NR_IRQS) {
 		seq_printf(p, "NMI: ");
-		for_each_cpu(j)
+		for_each_online_cpu(j)
 			seq_printf(p, "%10u ", nmi_count(j));
 		seq_putc(p, '\n');
 #ifdef CONFIG_X86_LOCAL_APIC
 		seq_printf(p, "LOC: ");
-		for_each_cpu(j)
+		for_each_online_cpu(j)
 			seq_printf(p, "%10u ",
 				per_cpu(irq_stat,j).apic_timer_irqs);
 		seq_putc(p, '\n');
_

Re: [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Shaohua Li]

Hi,
On Wed, 2005-08-31 at 20:13 +0800, Natalie.Protasevich@unisys.com wrote:
> Current IA32 CPU hotplug code doesn't allow bringing up processors
> that were not present in the boot configuration.  
> To make existing hot plug facility more practical for physical hot
> plug, possible processors should be encountered  
> during boot for potentual hot add/replace/remove. On ES7000, ACPI
> marks all the sockets that are empty or not assigned 
> to the partitionas as "disabled". The patch allows arrays/masks with
> APIC info for disabled processors to be  
> initialized. Then the OS can bring up a processor that was inserted in
> the socked and brought into configuration  
> during runtime.  
> To test the code, one can boot the system with maxcpu=1 and then bring
> the rest of the processors up, which was not  
> possible so far (only maxcpus number of nodes were created). 
> The patch also makes proc entry for interrupts dynamically change to
> only show current onlined processors.
Could we clean up the cpu_present_map a bit, like IA64 does? Eg, if a
new CPU is inserted, we allocated cpu id for it and set cpu_present_map.
Current alloc_cpu_id is just a workaround for suspend/resume use, but
isn't ok for physical cpu hotplug to me.

Thanks,
Shaohua

Re: [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Andi Kleen]

Hallo Natalie,

On Wednesday 31 August 2005 14:13, Natalie.Protasevich@unisys.com wrote:
> Current IA32 CPU hotplug code doesn't allow bringing up processors that
> were not present in the boot configuration. To make existing hot plug
> facility more practical for physical hot plug, possible processors should
> be encountered during boot for potentual hot add/replace/remove. On ES7000,
> ACPI marks all the sockets that are empty or not assigned to the
> partitionas as "disabled". 

Good idea. In fact I always hated the behaviour of the existing
hotplug code that assumes all possible CPUs can be hotplugged.
It would be much nicer to be told be the firmware what CPUs
are hotpluggable. It would be great if all ia32/x86-64 hotplug capable 
BIOS behaved like your.


>  	struct warm_boot_cpu_info info;
>  	struct work_struct task;
>  	int	apicid, ret;
> +	extern u8 bios_cpu_apicid[NR_CPUS];

This should be in some header.

>
>  	lock_cpu_hotplug();
> -	apicid = x86_cpu_to_apicid[cpu];
> +	apicid = bios_cpu_apicid[cpu];

Why this change? It seems unrelated.

>  	if (apicid == BAD_APICID) {
>  		ret = -ENODEV;
>  		goto exit;
> diff -puN arch/i386/mach-default/topology.c~hotcpu-i386
> arch/i386/mach-default/topology.c ---
> linux-2.6.13-rc6-mm2/arch/i386/mach-default/topology.c~hotcpu-i386	2005-08-
>31 04:17:20.957019600 -0700 +++
> linux-2.6.13-rc6-mm2-root/arch/i386/mach-default/topology.c	2005-08-31
> 04:22:13.020619184 -0700 @@ -76,7 +76,7 @@ static int __init
> topology_init(void)
>  	for_each_online_node(i)
>  		arch_register_node(i);
>
> -	for_each_present_cpu(i)
> +	for_each_cpu(i)

This looks wrong. The CPUs should be in the present mask
if it's present. Followup code similar.

BTW shouldn't there be some attribute in sysfs that says
"CPU disabled"?

-Andi

Re: [Hotplug_sig] [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Nathan Lynch]

Natalie.Protasevich@unisys.com wrote:

> +#ifdef CONFIG_HOTPLUG_CPU
> +	if (cpu_online(cpu)) {
> +#else
>  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> +#endif
>  		ret = -EINVAL;
>  		goto out;
>  	}

Why this change?  I think the cpu_present check is needed for ppc64
since it has non-present cpus in sysfs.

Re: [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Ashok Raj]

On Wed, Aug 31, 2005 at 05:13:10AM -0700, Natalie.Protasevich@unisys.com wrote:

Hi Natalie,

sorry for the late catchup... 

Just to make sure we use the cpu maps properly here is the current definition
iam not sure if you are breaking any of these assumptions, cause if you do
you will break existing implementations... so pardon for the verbosity.

cpu_possible_map - must include all possible cpus that can ever exist in this
                   instance of boot. This map is static, i.e you can grow
                   or remove bits without causing confution to the rest of the 
                   subsystem. We attempted to change, but there was not much
                   in return for the savings, for the complexity we would
                   add to make this map dynamic.

cpu_present_map - indicates that these are present and operational. OS
                  can decide if they should be brought up or not.

when CONFIG_HOTPLUG_CPU is *not* defined, then cpu_possible_map and 
cpu_present_map are the same. When CONFIG_HOTPLUG_CPU=y, then we extend
cpu_possible_map to cover the range of NR_CPUS, but cpu_present_map still shows
what is real. 

When a physical hotplug happens, cpu_present_map is updated by who ever manages
the physical hotplug. 
> 
> Current IA32 CPU hotplug code doesn't allow bringing up processors that were not present in the boot configuration. 
> To make existing hot plug facility more practical for physical hot plug, possible processors should be encountered 
> during boot for potentual hot add/replace/remove. On ES7000, ACPI marks all the sockets that are empty or not assigned
> to the partitionas as "disabled". The patch allows arrays/masks with APIC info for disabled processors to be 

This sounds like a cluge to me. The correct implementation would be you would 
need some sysmgmt deamon or something that works with the kernel to notify of 
new cpus and populate apicid and grow cpu_present_map. Making an assumption that
disabled APICID are valid for ES7000 sake is not a safe assumption.

> initialized. Then the OS can bring up a processor that was inserted in the socked and brought into configuration 
> during runtime. 
> To test the code, one can boot the system with maxcpu=1 and then bring the rest of the processors up, which was not 
> possible so far (only maxcpus number of nodes were created).
> The patch also makes proc entry for interrupts dynamically change to only show current onlined processors.
> 
> Signed-off-by: Natalie Protasevich  <Natalie.Protasevich@unisys.com>
> ---
> 
>  arch/i386/kernel/acpi/boot.c      |    2 ++
>  arch/i386/kernel/irq.c            |    8 ++++----
>  arch/i386/kernel/mpparse.c        |    4 ++++
>  arch/i386/kernel/smpboot.c        |    3 ++-
>  arch/i386/mach-default/topology.c |    4 ++--
>  kernel/cpu.c                      |    4 ++++
>  6 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff -puN arch/i386/kernel/acpi/boot.c~hotcpu-i386 arch/i386/kernel/acpi/boot.c
> --- linux-2.6.13-rc6-mm2/arch/i386/kernel/acpi/boot.c~hotcpu-i386	2005-08-31 04:17:20.832038600 -0700
> +++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/acpi/boot.c	2005-08-31 04:19:35.259602504 -0700
> @@ -255,9 +255,11 @@ acpi_parse_lapic(acpi_table_entry_header
>  
>  	acpi_table_print_madt_entry(header);
>  
> +#ifndef CONFIG_HOTPLUG_CPU
>  	/* no utility in registering a disabled processor */
>  	if (processor->flags.enabled == 0)
>  		return 0;
> +#endif

On same lines, the above config code seems not appropriate. When your platform
needs to hot-add a cpu, find a way to set these flags, you cant break
current behaviour as for a platform quirk!
>  
>  	x86_acpiid_to_apicid[processor->acpi_id] = processor->id;
>  
> diff -puN arch/i386/kernel/mpparse.c~hotcpu-i386 arch/i386/kernel/mpparse.c
> --- linux-2.6.13-rc6-mm2/arch/i386/kernel/mpparse.c~hotcpu-i386	2005-08-31 04:17:20.877031760 -0700
> +++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/mpparse.c	2005-08-31 04:20:49.297347056 -0700
> @@ -125,8 +125,10 @@ static void __init MP_processor_info (st
>   	int ver, apicid, cpu, found_bsp = 0;
>  	physid_mask_t tmp;
>   	
> +#ifndef CONFIG_HOTPLUG_CPU
>  	if (!(m->mpc_cpuflag & CPU_ENABLED))
>  		return;
> +#endif

Same here... platform quirk!

>  
>  	apicid = mpc_apic_id(m, translation_table[mpc_record]);
>  
> @@ -190,11 +192,13 @@ static void __init MP_processor_info (st
>  		return;
>  	}
>  
> +#ifndef CONFIG_HOTPLUG_CPU
>  	if (num_processors >= maxcpus) {
>  		printk(KERN_WARNING "WARNING: maxcpus limit of %i reached."
>  			" Processor ignored.\n", maxcpus); 
>  		return;
>  	}
> +#endif
>  	num_processors++;
>  	ver = m->mpc_apicver;
>  
> diff -puN arch/i386/kernel/smpboot.c~hotcpu-i386 arch/i386/kernel/smpboot.c
> --- linux-2.6.13-rc6-mm2/arch/i386/kernel/smpboot.c~hotcpu-i386	2005-08-31 04:17:20.924024616 -0700
> +++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/smpboot.c	2005-08-31 04:21:49.474198784 -0700
> @@ -1003,9 +1003,10 @@ int __devinit smp_prepare_cpu(int cpu)
>  	struct warm_boot_cpu_info info;
>  	struct work_struct task;
>  	int	apicid, ret;
> +	extern u8 bios_cpu_apicid[NR_CPUS];
>  
>  	lock_cpu_hotplug();
> -	apicid = x86_cpu_to_apicid[cpu];
> +	apicid = bios_cpu_apicid[cpu];
>  	if (apicid == BAD_APICID) {
>  		ret = -ENODEV;
>  		goto exit;
> diff -puN arch/i386/mach-default/topology.c~hotcpu-i386 arch/i386/mach-default/topology.c
> --- linux-2.6.13-rc6-mm2/arch/i386/mach-default/topology.c~hotcpu-i386	2005-08-31 04:17:20.957019600 -0700
> +++ linux-2.6.13-rc6-mm2-root/arch/i386/mach-default/topology.c	2005-08-31 04:22:13.020619184 -0700
> @@ -76,7 +76,7 @@ static int __init topology_init(void)
>  	for_each_online_node(i)
>  		arch_register_node(i);
>  
> -	for_each_present_cpu(i)
> +	for_each_cpu(i)

Nope. Should still be for present_cpus. with NR_CPUS large we would see 
way too many files in sysfs than what is really available. 

>  		arch_register_cpu(i);
>  	return 0;
>  }
> @@ -87,7 +87,7 @@ static int __init topology_init(void)
>  {
>  	int i;
>  
> -	for_each_present_cpu(i)
> +	for_each_cpu(i)
>  		arch_register_cpu(i);
>  	return 0;
>  }
> diff -puN kernel/cpu.c~hotcpu-i386 kernel/cpu.c
> --- linux-2.6.13-rc6-mm2/kernel/cpu.c~hotcpu-i386	2005-08-31 04:17:21.002012760 -0700
> +++ linux-2.6.13-rc6-mm2-root/kernel/cpu.c	2005-08-31 04:23:34.378250944 -0700
> @@ -158,7 +158,11 @@ int __devinit cpu_up(unsigned int cpu)
>  	if ((ret = down_interruptible(&cpucontrol)) != 0)
>  		return ret;
>  
> +#ifdef CONFIG_HOTPLUG_CPU
> +	if (cpu_online(cpu)) {
> +#else
>  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> +#endif

ditto.....
>  		ret = -EINVAL;
>  		goto out;
>  	}
> diff -puN arch/i386/kernel/irq.c~hotcpu-i386 arch/i386/kernel/irq.c
> --- linux-2.6.13-rc6-mm2/arch/i386/kernel/irq.c~hotcpu-i386	2005-08-31 04:17:21.047005920 -0700
> +++ linux-2.6.13-rc6-mm2-root/arch/i386/kernel/irq.c	2005-08-31 04:25:21.761926144 -0700
> @@ -248,7 +248,7 @@ int show_interrupts(struct seq_file *p, 
>  
>  	if (i == 0) {
>  		seq_printf(p, "           ");
> -		for_each_cpu(j)
> +		for_each_online_cpu(j)
>  			seq_printf(p, "CPU%d       ",j);
>  		seq_putc(p, '\n');
>  	}
> @@ -262,7 +262,7 @@ int show_interrupts(struct seq_file *p, 
>  #ifndef CONFIG_SMP
>  		seq_printf(p, "%10u ", kstat_irqs(i));
>  #else
> -		for_each_cpu(j)
> +		for_each_online_cpu(j)
>  			seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
>  #endif
>  		seq_printf(p, " %14s", irq_desc[i].handler->typename);
> @@ -276,12 +276,12 @@ skip:
>  		spin_unlock_irqrestore(&irq_desc[i].lock, flags);
>  	} else if (i == NR_IRQS) {
>  		seq_printf(p, "NMI: ");
> -		for_each_cpu(j)
> +		for_each_online_cpu(j)
>  			seq_printf(p, "%10u ", nmi_count(j));
>  		seq_putc(p, '\n');
>  #ifdef CONFIG_X86_LOCAL_APIC
>  		seq_printf(p, "LOC: ");
> -		for_each_cpu(j)
> +		for_each_online_cpu(j)
>  			seq_printf(p, "%10u ",
>  				per_cpu(irq_stat,j).apic_timer_irqs);
>  		seq_putc(p, '\n');
> _

-- 
Cheers,
Ashok Raj
- Open Source Technology Center

Re: [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Ashok Raj]

On Thu, Sep 01, 2005 at 10:45:10AM +0200, Andi Kleen wrote:
> Hallo Natalie,
> 
> On Wednesday 31 August 2005 14:13, Natalie.Protasevich@unisys.com wrote:
> > Current IA32 CPU hotplug code doesn't allow bringing up processors that
> > were not present in the boot configuration. To make existing hot plug
> > facility more practical for physical hot plug, possible processors should
> > be encountered during boot for potentual hot add/replace/remove. On ES7000,
> > ACPI marks all the sockets that are empty or not assigned to the
> > partitionas as "disabled". 
> 
> Good idea. In fact I always hated the behaviour of the existing
> hotplug code that assumes all possible CPUs can be hotplugged.
> It would be much nicer to be told be the firmware what CPUs
> are hotpluggable. It would be great if all ia32/x86-64 hotplug capable 
> BIOS behaved like your.
> 

Andi, you are getting mixed up with software only ability to offline with 
hardware eject capability. ACPI indicates ability to hotplug by the presence
of _EJD in the appropriate scope of the object. So ACPI does have ability to 
do what you mention above precicely, but the entire namespace is not known 
upfront since some could be dynamically loaded. Which is why we need to show 
the entire NR_CPUS as hotpluggable. 

Possibly we can keep cpu_possible_map as NR_CPUS only when support for 
PHYSICAL_CPU_HOTPLUG is present, otherwise we can keep it
cloned as cpu_present_map. (we dont have a generic PHYSICAL hotplug CONFIG
option today)

What CONFIG_HOTPLUG_CPU=y indicates is ability to offline a processor from the
kernel. It DOES NOT indicate physical hotpluggablity.  So we dont need any
hardware support (apart arch/kernel support) for this to work. Support
for physical hotplug is indicated via CONFIG_ACPI_HOTPLUG_CPU.

Be aware that suspend/resume folks using CPU hotplug to offline CPUS except
BSP need just the kernel support to offline. BIOS has nothing to do with 
being able to offline a CPU (preferably called as soft-removal).

Cheers,
ashok

RE: [Hotplug_sig] [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Protasevich, Natalie]

> Protasevich, Natalie wrote:
> > > > +#ifdef CONFIG_HOTPLUG_CPU
> > > > +	if (cpu_online(cpu)) {
> > > > +#else
> > > >  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> > > > +#endif
> > > >  		ret = -EINVAL;
> > > >  		goto out;
> > > >  	}
> > > 
> > > Why this change?  I think the cpu_present check is needed for
> > > ppc64 since it has non-present cpus in sysfs.
> > > 
> > 
> > The new processor was never brought up, its bit is only set in 
> > cpu_possible_map, but not in present map.
> 
> If a cpu is physically present and is capable of being 
> onlined it should be marked in cpu_present_map, please.  This 
> change would break ppc64; can you rework it?
>
OK, that has to be reworked then. That's what probably Shaohua meant
when mentioned that cpu_present_map has to be cleaned up... 
Thanks,
--Natalie

Re: [Hotplug_sig] [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Nathan Lynch]

Protasevich, Natalie wrote:
> > > +#ifdef CONFIG_HOTPLUG_CPU
> > > +	if (cpu_online(cpu)) {
> > > +#else
> > >  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> > > +#endif
> > >  		ret = -EINVAL;
> > >  		goto out;
> > >  	}
> > 
> > Why this change?  I think the cpu_present check is needed for 
> > ppc64 since it has non-present cpus in sysfs.
> > 
> 
> The new processor was never brought up, its bit is only set in
> cpu_possible_map, but not in present map. 

If a cpu is physically present and is capable of being onlined it
should be marked in cpu_present_map, please.  This change would break
ppc64; can you rework it?

RE: [Hotplug_sig] [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Protasevich, Natalie]

> > +#ifdef CONFIG_HOTPLUG_CPU
> > +	if (cpu_online(cpu)) {
> > +#else
> >  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> > +#endif
> >  		ret = -EINVAL;
> >  		goto out;
> >  	}
> 
> Why this change?  I think the cpu_present check is needed for 
> ppc64 since it has non-present cpus in sysfs.
> 

The new processor was never brought up, its bit is only set in
cpu_possible_map, but not in present map. 

        ... 
        if (boot_error) {
                /* Try to put things back the way they were before ...
*/
                unmap_cpu_to_logical_apicid(cpu);
                cpu_clear(cpu, cpu_callout_map); /* was set here
(do_boot_cpu()) */
                cpu_clear(cpu, cpu_initialized); /* was set by
cpu_init() */
                cpucount--;
        } else {
                x86_cpu_to_apicid[cpu] = apicid;
                cpu_set(cpu, cpu_present_map);  <=====================
        }
        ...
So if someone tries to boot a CPU up first time during runtime it always
fails this check.
Thanks,
--Natalie