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SubjectRe: [PATCH] Fix disk statistic reporting to include all disks
On Tue, Aug 29 2000, Linus Torvalds wrote:
> > Sounds sane, but what about drivers that don't really use the request
> > queue structure? Stuff like lvm, md, rd (with Neil's patch to fix the
> > lru_list deadlock), and probably new loop.
>
> Every single driver must have a request_queue: as far as the ll_rw_block
> layer is concerned, a NULL request-queue means that the device doesn't
> exist. It will even print out a message saying so..
>
> I'm not sure what you mean about lvm/md/rd not having request queues.

Maybe I wasn't very clear... What I mean is that drivers that use
blk_queue_make_request (such as md) are handed buffers directly and
don't get requests added to their queues in the regular sense, instead
they remap b_rdev before ll_rw_blk gets the queue for the device and
adds them to the destination queue.

So per request accounting isn't done for md currently, although (as per
your next mail) I do agree that having statistics for both makes sense.

--
* Jens Axboe <axboe@suse.de>
* SuSE Labs
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