On 2011-04-18 11:40, Hannes Reinecke wrote:

On 04/18/2011 11:19 AM, hch@infradead.org wrote:

quoted

Btw, I really start to wonder if the request level is the right place
to do this on-stack plugging.  Wouldn't it be better to just plug
bios in the on-stack queue?  That way we could also stop doing the
special case merging when adding to the plug list, and leave all the
merging / I/O schedule logic in the __make_request path.  Probably
not .39 material, but worth a prototype?

Also what this dicussion brought up is that the block layer data
structures are highly confusing.  Using a small subset of the
request_queue also for make_request based driver just doesn't make
sense.  It seems like we should try to migrate the required state
to struct gendisk, and submit I/O through a block_device_ops.submit
method, leaving the request_queue as an internal abstraction for
the request based drivers.

Good point.
It would also help us we the device-mapper redesign agk and myself 
discussed at LSF. Having a block_device_ops.submit function would
allow us remap the actual request queue generically; and we would 
even be able to address more than one request queue, which sounds 
awfully similar to what Jens is trying to do ...

The multiqueue bits would still have one request_queue, but multiple
queueing structures (I called those blk_queue_ctx, iirc).

-- 
Jens Axboe