On Fri, Sep 23, 2011 at 07:49:56AM +1000, Dave Chinner wrote: > On Thu, Sep 22, 2011 at 10:14:57AM -0400, Christoph Hellwig wrote: > > By default, a wq guarantees non-reentrance only on the same > > CPU. A work item may not be executed concurrently on the same > > CPU by multiple workers but is allowed to be executed > > concurrently on multiple CPUs. This flag makes sure > > non-reentrance is enforced across all CPUs. Work items queued > > to a non-reentrant wq are guaranteed to be executed by at most > > one worker system-wide at any given time. > > > > So this still seems to preferable for the ail workqueue, and should be > > able to replace the XFS_AIL_PUSHING_BIT protections. > > No, we can't. WQ_NON_REENTRANT only protects against concurrency on > the same CPU, not across all CPUs - it still allows concurrent > per-CPU work processing on the same work item. Non concurrently for a given work_struct on the same CPU is the default, WQ_NON_REENTRANT extents that to not beeing exectuted concurrently at all. Check the documentation above again, or the code - just look for the only occurance of WQ_NON_REENTRANT in kernel/workqueue.c and the surronuding code (e.g. find_worker_executing_work and the current_work field in struct worker) > However, we want only a *single* AIL worker instance executing per > filesystem, not per-cpu per filesystem. Concurrent per-filesystem > workers will simply bash on the AIL lock trying to walk the AIL at > the same time, and this is precisely the issue the single AIL worker > setup is avoiding. The XFS_AIL_PUSHING_BIT is what enforces the > single per-filesystem push worker running at any time. I think that's exactly what WQ_NON_REENTRANT is intended for. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
