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Re: [dm-devel] [PATCH 05/10] block: remove per-queue plugging



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

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
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