[PATCH] powerpc/pseries: Don't attempt to acquire drc during memory hot add for assigned lmbs

[John Allen]

On 08/24/2017 05:33 AM, Michael Ellerman wrote:
> John Allen <jallen at linux.vnet.ibm.com> writes:
> 
>> Check if an LMB is assigned before attempting to call dlpar_acquire_drc in
>> order to avoid any unnecessary rtas calls. This substantially reduces the
>> running time of memory hot add on lpars with large amounts of memory.
>>
>> Signed-off-by: John Allen <jallen at linux.vnet.ibm.com>
> 
> I'll add:
> 
>   Fixes: c21f515c7436 ("powerpc/pseries: Make the acquire/release of the drc for memory a seperate step")
> 
> ?

Yes, thanks.

> 
> How bad is the slow down, do we need to backport to stable/distros?

On an lpar with 16 TB of memory assigned, I observed that adding 1 GB of
memory took several minutes without this fix and improved to several
seconds with this fix. Yep, this will need to be backported. Memory hotplug
performance is a hot issue for our team right now and we'll want to have
solid performance improvement to give to customers relatively soon.

> 
> cheers
> 
>