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

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Date:	Mon, 18 Apr 2011 11:47:39 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Hannes Reinecke <hare@...e.de>
CC:	device-mapper development <dm-devel@...hat.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	Mike Snitzer <snitzer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alasdair G Kergon <agk@...hat.com>
Subject: Re: [dm-devel] [PATCH 05/10] block: remove per-queue plugging

On 2011-04-18 11:40, Hannes Reinecke wrote:
> On 04/18/2011 11:19 AM, hch@...radead.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 ...

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

-- 
Jens Axboe

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