On Mon, Mar 25, 2013 at 01:58:04PM -0500, Nathan Fontenot wrote: > From: Jesse Larrew <jlar...@linux.vnet.ibm.com> > > The new PRRN firmware feature allows CPU and memory resources to be > transparently reassigned across NUMA boundaries. When this happens, the > kernel must update the node maps to reflect the new affinity > information. > > Although the NUMA maps can be protected by locking primitives during the > update itself, this is insufficient to prevent concurrent accesses to these > structures. Since cpumask_of_node() hands out a pointer to these > structures, they can still be modified outside of the lock. Furthermore, > tracking down each usage of these pointers and adding locks would be quite > invasive and difficult to maintain. > > Situations like these are best handled using stop_machine(). Since the NUMA > affinity updates are exceptionally rare events, this approach has the > benefit of not adding any overhead while accessing the NUMA maps during > normal operation.
I notice you do one stop_machine() call for every cpu whose affinity has changed. Couldn't we update the affinity for them all in one stop_machine call? Given that stopping the whole machine can be quite slow, wouldn't it be better to do one call rather than potentially many? Paul. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
