[PATCH] powerpc: Linux cannot run with 0 cores

[PATCH] powerpc: Linux cannot run with 0 cores

[Anton Blanchard]

If we configure with CONFIG_SMP=n or set NR_CPUS less than the number of
SMT threads we will set the max cores property to 0 in the
ibm,client-architecture-support structure. On new versions of firmware that
understand this property it obliges and terminates our partition.

Use DIV_ROUND_UP so we handle not only the CONFIG_SMP=n case but also the
case where NR_CPUS isn't a multiple of the number of SMT threads.

Signed-off-by: Anton Blanchard <anton@samba.org>
---

Index: linux-2.6/arch/powerpc/kernel/prom_init.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/prom_init.c	2010-06-17 09:08:20.000000000 +1000
+++ linux-2.6/arch/powerpc/kernel/prom_init.c	2010-06-17 09:10:02.000000000 +1000
@@ -872,7 +872,7 @@ static void __init prom_send_capabilitie
 				    "ibm_architecture_vec structure inconsistent: 0x%x !\n",
 				    *cores);
 		} else {
-			*cores = NR_CPUS / prom_count_smt_threads();
+			*cores = DIV_ROUND_UP(NR_CPUS, prom_count_smt_threads());
 			prom_printf("Max number of cores passed to firmware: 0x%x\n",
 				    (unsigned long)*cores);
 		}

Re: [PATCH] powerpc: Linux cannot run with 0 cores

[Paul E. McKenney]

On Fri, Jun 18, 2010 at 10:33:06AM +1000, Anton Blanchard wrote:
> 
> If we configure with CONFIG_SMP=n or set NR_CPUS less than the number of
> SMT threads we will set the max cores property to 0 in the
> ibm,client-architecture-support structure. On new versions of firmware that
> understand this property it obliges and terminates our partition.
> 
> Use DIV_ROUND_UP so we handle not only the CONFIG_SMP=n case but also the
> case where NR_CPUS isn't a multiple of the number of SMT threads.

Thank you, Anton!!!

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

(Will test as soon as the system that hit this becomes available.)

> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
> 
> Index: linux-2.6/arch/powerpc/kernel/prom_init.c
> ===================================================================
> --- linux-2.6.orig/arch/powerpc/kernel/prom_init.c	2010-06-17 09:08:20.000000000 +1000
> +++ linux-2.6/arch/powerpc/kernel/prom_init.c	2010-06-17 09:10:02.000000000 +1000
> @@ -872,7 +872,7 @@ static void __init prom_send_capabilitie
>  				    "ibm_architecture_vec structure inconsistent: 0x%x !\n",
>  				    *cores);
>  		} else {
> -			*cores = NR_CPUS / prom_count_smt_threads();
> +			*cores = DIV_ROUND_UP(NR_CPUS, prom_count_smt_threads());
>  			prom_printf("Max number of cores passed to firmware: 0x%x\n",
>  				    (unsigned long)*cores);
>  		}