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[PATCH] arch/sparc: support NR_CPUS = 4096

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  [PATCH] arch/sparc: support NR_CPUS = 4096 Jane Chu <jane.chu@oracle.com> - 2017-06-01 23:40 +0200
    Re: [PATCH] arch/sparc: support NR_CPUS = 4096 David Miller <davem@davemloft.net> - 2017-06-05 01:50 +0200
      Re: [PATCH] arch/sparc: support NR_CPUS = 4096 jane.chu@oracle.com - 2017-06-05 21:20 +0200
      Re: [PATCH] arch/sparc: support NR_CPUS = 4096 jane.chu@oracle.com - 2017-06-05 23:40 +0200
        Re: [PATCH] arch/sparc: support NR_CPUS = 4096 David Miller <davem@davemloft.net> - 2017-06-06 00:00 +0200

#1655777 — [PATCH] arch/sparc: support NR_CPUS = 4096

Linux SPARC64 limits NR_CPUS to 4064 because init_cpu_send_mondo_info()
only allocates a single page for NR_CPUS mondo entries. Thus we cannot
use all 4096 CPUs on some SPARC platforms.

To fix, allocate (2^order) pages where order is set according to the size
of cpu_list for possible cpus. Since cpu_list_pa and cpu_mondo_block_pa
are not used in asm code, there are no imm13 offsets from the base PA
that will break because they can only reach one page.

Orabug: 25505750

Signed-off-by: Jane Chu <jane.chu@oracle.com>

Reviewed-by: Bob Picco <bob.picco@oracle.com>
Reviewed-by: Atish Patra <atish.patra@oracle.com>
---
 arch/sparc/Kconfig         |    4 ++--
 arch/sparc/kernel/irq_64.c |    8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 58243b0..4399be7 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -192,9 +192,9 @@ config NR_CPUS
 	int "Maximum number of CPUs"
 	depends on SMP
 	range 2 32 if SPARC32
-	range 2 1024 if SPARC64
+	range 2 4096 if SPARC64
 	default 32 if SPARC32
-	default 64 if SPARC64
+	default 4096 if SPARC64
 
 source kernel/Kconfig.hz
 
diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
index 4d0248a..5b19108 100644
--- a/arch/sparc/kernel/irq_64.c
+++ b/arch/sparc/kernel/irq_64.c
@@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
 {
 #ifdef CONFIG_SMP
 	unsigned long page;
+	unsigned int order;
 
-	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
-
-	page = get_zeroed_page(GFP_KERNEL);
+	order = get_order(num_possible_cpus() * sizeof(u16) + 64);
+	page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
 	if (!page) {
-		prom_printf("SUN4V: Error, cannot allocate cpu mondo page.\n");
+		prom_printf("SUN4V: Error, cannot allocate cpu mondo pages.\n");
 		prom_halt();
 	}
 
-- 
1.7.1

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#1657188

From: Jane Chu <jane.chu@oracle.com>
Date: Thu,  1 Jun 2017 15:39:13 -0600

> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
> index 4d0248a..5b19108 100644
> --- a/arch/sparc/kernel/irq_64.c
> +++ b/arch/sparc/kernel/irq_64.c
> @@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
>  {
>  #ifdef CONFIG_SMP
>  	unsigned long page;
> +	unsigned int order;
>  
> -	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
> -
> -	page = get_zeroed_page(GFP_KERNEL);
> +	order = get_order(num_possible_cpus() * sizeof(u16) + 64);
> +	page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>  	if (!page) {

The only reason we allocated these two items together was because it
was convenient and it all fit into a single page.

Since it now doesn't, it makes sense to split it up.

Simply use a single page for the cpu_list_pa and kzalloc for the
cpu_mondo_block.

This also allows to keep the BUILD_BUG_ON(), which I really wish
you hadn't tried to remove.

static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
{
#ifdef CONFIG_SMP
	unsigned long page;
	void *mondo;

	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);

	mondo = kzalloc(64, GFP_KERNEL);
	if (!mondo) {
		prom_printf("SUN4V: Error, cannot allocate mondo block.\n");
		prom_halt();
	}
	tb->cpu_mondo_block_pa = __pa(mondo);

	page = get_zeroed_page(GFP_KERNEL);
	if (!page) {
		prom_printf("SUN4V: Error, cannot allocate cpu list page.\n");
		prom_halt();
	}
	tb->cpu_list_pa = __pa(page);
#endif
}

Thanks.

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#1658085

Hi, David,


On 06/04/2017 04:46 PM, David Miller wrote:
> From: Jane Chu <jane.chu@oracle.com>
> Date: Thu,  1 Jun 2017 15:39:13 -0600
>
>> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
>> index 4d0248a..5b19108 100644
>> --- a/arch/sparc/kernel/irq_64.c
>> +++ b/arch/sparc/kernel/irq_64.c
>> @@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
>>   {
>>   #ifdef CONFIG_SMP
>>   	unsigned long page;
>> +	unsigned int order;
>>   
>> -	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
>> -
>> -	page = get_zeroed_page(GFP_KERNEL);
>> +	order = get_order(num_possible_cpus() * sizeof(u16) + 64);
>> +	page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>>   	if (!page) {
> The only reason we allocated these two items together was because it
> was convenient and it all fit into a single page.
>
> Since it now doesn't, it makes sense to split it up.
>
> Simply use a single page for the cpu_list_pa and kzalloc for the
> cpu_mondo_block.
>
> This also allows to keep the BUILD_BUG_ON(), which I really wish
> you hadn't tried to remove.

Good point!  I will just add a comment for future maintenance that
the mondo trap block needs to be 64byte aligned.
>
> static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
> {
> #ifdef CONFIG_SMP
> 	unsigned long page;
> 	void *mondo;
>
> 	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);
>
> 	mondo = kzalloc(64, GFP_KERNEL);
> 	if (!mondo) {
> 		prom_printf("SUN4V: Error, cannot allocate mondo block.\n");
> 		prom_halt();
> 	}
> 	tb->cpu_mondo_block_pa = __pa(mondo);
>
> 	page = get_zeroed_page(GFP_KERNEL);
> 	if (!page) {
> 		prom_printf("SUN4V: Error, cannot allocate cpu list page.\n");
> 		prom_halt();
> 	}
> 	tb->cpu_list_pa = __pa(page);
> #endif
> }

Thanks a lot!

-jane

>
> Thanks.

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#1658160

Hi,

I have a question about a checkpatch.pl warning against the

use of NR_CPUS -

$ ./scripts/checkpatch.pl diff.patch
WARNING: usage of NR_CPUS is often wrong - consider using 
cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc
#14: FILE: arch/sparc/kernel/irq_64.c:1039:
+       BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);

num_possible_cpus() is the hard limit on a domain without platform reboot,

it is capped by both NR_CPUS and 'max_cpus' (a platform property in the

machine description).  So it is theoretically possible to have NR_CPUS>4096

but num_possible_cpus() < 4096 -- a scenario I think we'd prefer to reject.

Is it okay to ignore the checkpatch.pl warning in this case?

thanks,

-jane


On 06/04/2017 04:46 PM, David Miller wrote:
> From: Jane Chu <jane.chu@oracle.com>
> Date: Thu,  1 Jun 2017 15:39:13 -0600
>
>> diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
>> index 4d0248a..5b19108 100644
>> --- a/arch/sparc/kernel/irq_64.c
>> +++ b/arch/sparc/kernel/irq_64.c
>> @@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
>>   {
>>   #ifdef CONFIG_SMP
>>   	unsigned long page;
>> +	unsigned int order;
>>   
>> -	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
>> -
>> -	page = get_zeroed_page(GFP_KERNEL);
>> +	order = get_order(num_possible_cpus() * sizeof(u16) + 64);
>> +	page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>>   	if (!page) {
> The only reason we allocated these two items together was because it
> was convenient and it all fit into a single page.
>
> Since it now doesn't, it makes sense to split it up.
>
> Simply use a single page for the cpu_list_pa and kzalloc for the
> cpu_mondo_block.
>
> This also allows to keep the BUILD_BUG_ON(), which I really wish
> you hadn't tried to remove.
>
> static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
> {
> #ifdef CONFIG_SMP
> 	unsigned long page;
> 	void *mondo;
>
> 	BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);
>
> 	mondo = kzalloc(64, GFP_KERNEL);
> 	if (!mondo) {
> 		prom_printf("SUN4V: Error, cannot allocate mondo block.\n");
> 		prom_halt();
> 	}
> 	tb->cpu_mondo_block_pa = __pa(mondo);
>
> 	page = get_zeroed_page(GFP_KERNEL);
> 	if (!page) {
> 		prom_printf("SUN4V: Error, cannot allocate cpu list page.\n");
> 		prom_halt();
> 	}
> 	tb->cpu_list_pa = __pa(page);
> #endif
> }
>
> Thanks.

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#1658171

From: jane.chu@oracle.com
Date: Mon, 5 Jun 2017 14:32:10 -0700

> Is it okay to ignore the checkpatch.pl warning in this case?

I absolutely think you can ignore this warning.

Thanks.

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