Re: [PATCH2/11] Add PRRN Event Handler

[Nathan Fontenot <nfont@linux.vnet.ibm.com>]

On 03/14/2013 03:51 AM, Paul Mackerras wrote:
> On Fri, Mar 08, 2013 at 10:00:09PM -0600, Nathan Fontenot wrote:
>> From: Jesse Larrew <jlarrew@linux.vnet.ibm.com>
>>
>> A PRRN event is signaled via the RTAS event-scan mechanism, which
>> returns a Hot Plug Event message "fixed part" indicating "Platform
>> Resource Reassignment". In response to the Hot Plug Event message,
>> we must call ibm,update-nodes to determine which resources were
>> reassigned and then ibm,update-properties to obtain the new affinity
>> information about those resources.
>>
>> The PRRN event-scan RTAS message contains only the "fixed part" with
>> the "Type" field set to the value 160 and no Extended Event Log. The
>> four-byte Extended Event Log Length field is repurposed (since no
>> Extended Event Log message is included) to pass the "scope" parameter
>> that causes the ibm,update-nodes to return the nodes affected by the
>> specific resource reassignment.
>>
>> This patch adds a handler in rtasd for PRRN RTAS events. The function
>> pseries_devicetree_update() (from mobility.c) is used to make the
>> ibm,update-nodes/ibm,update-properties RTAS calls. Updating the NUMA maps
>> (handled by a subsequent patch) will require significant processing,
>> so pseries_devicetree_update() is called from an asynchronous workqueue
>> to allow rtasd to continue processing events.
>>
>> Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
> 
> [snip]
> 
>> +static s32 update_scope;
> 
> Do we have a guarantee that there can only be one of these events
> outstanding at a time?  If so it would be nice to document that in a
> comment next to this declaration, so we know in future that this is
> why this is safe.
> 

We only allow for one event to be outstanding. When a PRRN Event is
received we flush any work currently queued up and add the new event
event to the workqueue (see prrn_schedule_work() from the patch).

As I understand flush_work(), this would wait for any work in flight
to complete, then remove all work before returning. I'll add a comment
and update the patch description.

-Nathan