[v2] powerpc/numa: add ability to disable and debug topology updates

[Michael Ellerman]

On Thu, 2014-09-10 at 23:42:15 UTC, Nishanth Aravamudan wrote:
> We have hit a few customer issues with the topology update code (VPHN
> and PRRN). It would be nice to be able to debug the notifications coming
> from the hypervisor in both cases to the LPAR, as well as to disable
> responding to the notifications at boot-time, to narrow down the source
> of the problems. Add a basic level of such functionality, similar to the
> numa= command-line parameter. We already have a toggle in
> /proc/powerpc/topology_updates that allows run-time enabling/disabling,
> so the updates can be started at run-time if desired. But the bugs we've
> run into have occured during boot or very shortly after coming to login,
> and have resulted in a broken NUMA topology.

Thanks Nish, a couple of minor nits.

> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index e28c21ba862d..ad240a41d3e4 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -45,6 +45,7 @@ static char *cmdline __initdata;
>  
>  static int numa_debug;
>  #define dbg(args...) if (numa_debug) { printk(KERN_INFO args); }
> +#define pr_fmt(fmt) "numa: " fmt

This needs to come before printk.h to take effect, typically it goes before all
headers.

> @@ -1160,6 +1161,22 @@ static int __init early_numa(char *p)
>  }
>  early_param("numa", early_numa);
>  
> +static int topology_updates_enabled = 1;

bool ?

> +static int __init early_topology_updates(char *p)
> +{
> +	if (!p)
> +		return 0;
> +
> +	if (strstr(p, "off")) {

You're better off using strcmp. Using strstr() is nice if you need to support
multiple values, but it's sloppy otherwise. This will match "offset",
"smirnoff" etc.

> @@ -1807,7 +1836,9 @@ static const struct file_operations topology_ops = {
>  
>  static int topology_update_init(void)
>  {
> -	start_topology_update();
> +	/* Do not poll for changes if disabled at boot */
> +	if (topology_updates_enabled)
> +		start_topology_update();

Newline please!

>  	if (!proc_create("powerpc/topology_updates", 0644, NULL, &topology_ops))
>  		return -ENOMEM;

cheers