On Wed, 2005-04-20 at 16:40 +0900, Tejun Heo wrote: > Hello, Jens. > > On Wed, Apr 20, 2005 at 08:30:10AM +0200, Jens Axboe wrote: > > Do it on requeue, please - not on the initial spotting of the request. > > This is the reworked version of the patch. It sets REQ_SOFTBARRIER > in two places - in elv_next_request() on BLKPREP_DEFER and in > blk_requeue_request(). > > Other patches apply cleanly with this patch or the original one and > the end result is the same, so take your pick. :-) > I'm not sure that you need *either* one. As far as I'm aware, REQ_SOFTBARRIER is used when feeding requests into the top of the block layer, and is used to guarantee the device driver gets the requests in a specific ordering. When dealing with the requests at the other end (ie. elevator_next_req_fn, blk_requeue_request), then ordering does not change. That is - if you call elevator_next_req_fn and don't dequeue the request, then that's the same request you'll get next time. And blk_requeue_request will push the request back onto the end of the queue in a LIFO manner. So I think adding barriers, apart from not doing anything, confuses the issue because it suggests there *could* be reordering without them. Or am I completely wrong? It's been a while since I last got into the code. -- SUSE Labs, Novell Inc. - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
