On Fri, Aug 13, 2010 at 06:07:13PM -0700, Jeremy Fitzhardinge wrote: > On 08/12/2010 05:41 AM, Tejun Heo wrote: > > Barrier is deemed too heavy and will soon be replaced by FLUSH/FUA > > requests. Deprecate barrier. All REQ_HARDBARRIERs are failed with > > -EOPNOTSUPP and blk_queue_ordered() is replaced with simpler > > blk_queue_flush(). > > > > blk_queue_flush() takes combinations of REQ_FLUSH and FUA. If a > > device has write cache and can flush it, it should set REQ_FLUSH. If > > the device can handle FUA writes, it should also set REQ_FUA. > > Christoph, do these two patches (parts 2 and 3) make xen-blkfront > correct WRT barriers/flushing as far as your concerned? If all your backends handle a zero-length BLKIF_OP_WRITE_BARRIER request it is a fully correct, but rather suboptimal implementation. To get all the benefit of the new non-draining barriers you'll need a new If all your backends handle a zero-length BLKIF_OP_FLUSH request that only flushes the cache, but has no ordering side effects. Note that the quite suboptimal here means not as good as the new barrier implementation, but it shouldn't be notiably worse than the old one for Xen. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
