On Fri, May 08 2009, Tejun Heo wrote: > Hello, > > Upon ack, please pull from the following git tree. > > git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git block-peek-fetch > > Block layer has allowed two different models of request processing. > elv_next_request() is used to peek at the top of the queue, after > peeking, a LLD could start processing it immediately or dequeue and > then start processing. > > The non-dequeuing behavior is mostly useful for simpler device drivers > (usually PIO based) which process requests on segment basis. By using > the block layer queue tip as the current request pointer, they don't > have to care about request boundaries and just process things > segment-by-segment. > > However, this dual mode of operations complicates and ambiguates block > layer API. Block layer can't tell whether a request has begun > processing or not in deterministic manner. This makes accounting > inaccurate and implementing high level features in block layer > difficult. For example, it isn't clear when a block layer timeout > timer should be started or how queue queiscing for EH should be > implemented. Even when problems can be worked aroudn, it makes the > implementation fragile. > > Although allowing llds ignore request boundaries makes things simpler > for certain drivers, the number of drivers benefit form it aren't too > many and driver stacks which are even mildly complex have to deal with > request boundaries anyway. Also, the benefit itself isn't that > significant. In most cases, it is just another way of doing things > rather than the definitively better way. IOW, if there were no such > alternative, nobody would have missed it. > > This patchset converts all block layer llds to dequeuing model and > then clean up API to simplify a bit and enforce dequeueing model. > This patchset contains the following patches. Glad this finally got completed, thanks a lot Tejun! Applied. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
