[PATCH] powerpc: ONLINE to OFFLINE CPU state transition during removal

[Vaidyanathan Srinivasan]

* Robert Jennings <rcj at linux.vnet.ibm.com> [2010-07-22 21:43:44]:

> If a CPU remove is attempted using the 'release' interface on hardware
> which supports extended cede, the CPU will be put in the INACTIVE state
> rather than the OFFLINE state due to the default preferred_offline_state
> in that situation.  In the INACTIVE state it will fail to be removed.
> 
> This patch changes the preferred offline state to OFFLINE when an CPU is
> in the ONLINE state.  After cpu_down() is called in dlpar_offline_cpu()
> the CPU will be OFFLINE and CPU removal can continue.

Hi Robert,

Thanks for the patch.  In dlpar operation, we would offline the CPU
first using the sysfs online file and then write to the sysfs release
file to complete the sequence right?  The current code in
dlpar_offline_cpu() would work as long as the cpu is in either
inactive state or offline state (in case of unsupported platform).

Is the dlpar tools being changed to complete the operation with one
sysfs write to release file?

> Signed-off-by: Robert Jennings <rcj at linux.vnet.ibm.com>
> 
> ---
> 
> diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
> index d71e585..227c1c3 100644
> --- a/arch/powerpc/platforms/pseries/dlpar.c
> +++ b/arch/powerpc/platforms/pseries/dlpar.c
> @@ -463,6 +463,7 @@ static int dlpar_offline_cpu(struct device_node *dn)
>  				break;
> 
>  			if (get_cpu_current_state(cpu) == CPU_STATE_ONLINE) {
> +				set_preferred_offline_state(cpu, CPU_STATE_OFFLINE);
>  				cpu_maps_update_done();
>  				rc = cpu_down(cpu);
>  				if (rc)

The patch looks good.  Will need to test out the various scenarios so
that the preferred_offline_state do not get flipped before cpu_down()
is called.  This is unlikely, but still we need to validate
a concurrent sysfs online file write and sysfs release file write.

--Vaidy