[RFC][PATCH] powerpc: respect how command line nr_cpus is set

[RFC][PATCH] powerpc: respect how command line nr_cpus is set

[Kumar Gala]

We should utilize nr_cpus as the max # of CPUs that we can have present
instead of NR_CPUS.  This way we actually respect how nr_cpus is set on
the command line rather than ignoring it.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
---
I think this is what we should be doing, but would like someone else to take
a look.

- k

 arch/powerpc/kernel/setup-common.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index 21f30cb..fedf813 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -424,7 +424,7 @@ void __init smp_setup_cpu_maps(void)
 
 	DBG("smp_setup_cpu_maps()\n");
 
-	while ((dn = of_find_node_by_type(dn, "cpu")) && cpu < NR_CPUS) {
+	while ((dn = of_find_node_by_type(dn, "cpu")) && cpu < nr_cpu_ids) {
 		const int *intserv;
 		int j, len;
 
@@ -443,7 +443,7 @@ void __init smp_setup_cpu_maps(void)
 				intserv = &cpu;	/* assume logical == phys */
 		}
 
-		for (j = 0; j < nthreads && cpu < NR_CPUS; j++) {
+		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
 			DBG("    thread %d -> cpu %d (hard id %d)\n",
 			    j, cpu, intserv[j]);
 			set_cpu_present(cpu, true);
@@ -483,12 +483,12 @@ void __init smp_setup_cpu_maps(void)
 		if (cpu_has_feature(CPU_FTR_SMT))
 			maxcpus *= nthreads;
 
-		if (maxcpus > NR_CPUS) {
+		if (maxcpus > nr_cpu_ids) {
 			printk(KERN_WARNING
 			       "Partition configured for %d cpus, "
 			       "operating system maximum is %d.\n",
-			       maxcpus, NR_CPUS);
-			maxcpus = NR_CPUS;
+			       maxcpus, nr_cpu_ids);
+			maxcpus = nr_cpu_ids;
 		} else
 			printk(KERN_INFO "Partition configured for %d cpus.\n",
 			       maxcpus);
-- 
1.7.3.4

Re: [RFC][PATCH] powerpc: respect how command line nr_cpus is set

[Benjamin Herrenschmidt]

On Wed, 2011-05-04 at 15:17 -0500, Kumar Gala wrote:
> We should utilize nr_cpus as the max # of CPUs that we can have present
> instead of NR_CPUS.  This way we actually respect how nr_cpus is set on
> the command line rather than ignoring it.
> 
> Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
> ---
> I think this is what we should be doing, but would like someone else to take
> a look.

The main question I have is should max_cpus absolutely limit the number
of possible CPUs or should it limit the number that get automatically
onlined at boot, potentially letting us bring the rest online later on ?

Cheers,
Ben.

> - k
> 
>  arch/powerpc/kernel/setup-common.c |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 21f30cb..fedf813 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -424,7 +424,7 @@ void __init smp_setup_cpu_maps(void)
>  
>  	DBG("smp_setup_cpu_maps()\n");
>  
> -	while ((dn = of_find_node_by_type(dn, "cpu")) && cpu < NR_CPUS) {
> +	while ((dn = of_find_node_by_type(dn, "cpu")) && cpu < nr_cpu_ids) {
>  		const int *intserv;
>  		int j, len;
>  
> @@ -443,7 +443,7 @@ void __init smp_setup_cpu_maps(void)
>  				intserv = &cpu;	/* assume logical == phys */
>  		}
>  
> -		for (j = 0; j < nthreads && cpu < NR_CPUS; j++) {
> +		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
>  			DBG("    thread %d -> cpu %d (hard id %d)\n",
>  			    j, cpu, intserv[j]);
>  			set_cpu_present(cpu, true);
> @@ -483,12 +483,12 @@ void __init smp_setup_cpu_maps(void)
>  		if (cpu_has_feature(CPU_FTR_SMT))
>  			maxcpus *= nthreads;
>  
> -		if (maxcpus > NR_CPUS) {
> +		if (maxcpus > nr_cpu_ids) {
>  			printk(KERN_WARNING
>  			       "Partition configured for %d cpus, "
>  			       "operating system maximum is %d.\n",
> -			       maxcpus, NR_CPUS);
> -			maxcpus = NR_CPUS;
> +			       maxcpus, nr_cpu_ids);
> +			maxcpus = nr_cpu_ids;
>  		} else
>  			printk(KERN_INFO "Partition configured for %d cpus.\n",
>  			       maxcpus);

Re: [RFC][PATCH] powerpc: respect how command line nr_cpus is set

[Kumar Gala]

On May 4, 2011, at 9:25 PM, Benjamin Herrenschmidt wrote:

> On Wed, 2011-05-04 at 15:17 -0500, Kumar Gala wrote:
>> We should utilize nr_cpus as the max # of CPUs that we can have =
present
>> instead of NR_CPUS.  This way we actually respect how nr_cpus is set =
on
>> the command line rather than ignoring it.
>>=20
>> Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
>> ---
>> I think this is what we should be doing, but would like someone else =
to take
>> a look.
>=20
> The main question I have is should max_cpus absolutely limit the =
number
> of possible CPUs or should it limit the number that get automatically
> onlined at boot, potentially letting us bring the rest online later on =
?
>=20
> Cheers,
> Ben.

=46rom Documentation/kernel-parameters.txt:

        nr_cpus=3D        [SMP] Maximum number of processors that an SMP =
kernel
                        could support.  nr_cpus=3Dn : n >=3D 1 limits =
the kernel to
                        supporting 'n' processors. Later in runtime you =
can not
                        use hotplug cpu feature to put more cpu back to =
online.
                        just like you compile the kernel NR_CPUS=3Dn

Which makes me think we should have max_cpus be an absolute limit.

- k=

Re: [RFC][PATCH] powerpc: respect how command line nr_cpus is set

[Benjamin Herrenschmidt]

> From Documentation/kernel-parameters.txt:
> 
>         nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
>                         could support.  nr_cpus=n : n >= 1 limits the kernel to
>                         supporting 'n' processors. Later in runtime you can not
>                         use hotplug cpu feature to put more cpu back to online.
>                         just like you compile the kernel NR_CPUS=n
> 
> Which makes me think we should have max_cpus be an absolute limit.

Ok, looks like I've been confusing nr_cpus= vs. max_cpus= or something
like that.

I'll have a look at your patch later today.

Cheers,
Ben.

Re: [RFC] powerpc: respect how command line nr_cpus is set

[Milton Miller]

On Wed, 04 May 2011 around 10:17:37 -0000, Kumar Gala wrote:
> We should utilize nr_cpus as the max # of CPUs that we can have present
> instead of NR_CPUS.  This way we actually respect how nr_cpus is set on
> the command line rather than ignoring it.
> 
> Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
> 
> ---
> I think this is what we should be doing, but would like someone else to take
> a look.
> 
> - k
> 
>  arch/powerpc/kernel/setup-common.c |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 

This looks very similar to my patch at
http://patchwork.ozlabs.org/patch/95080/ except I also updated the
comment. Also, the variable is nr_cpu_ids while the parameter
is nr_cpus=, the first instance in in the changelog is referring to
the variable while the second is the parameter.

Sorry I took me so long get that part of my series tested and posted.

milton