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

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Message-ID: <4DAC070C.6010403@suse.de>
Date:	Mon, 18 Apr 2011 11:40:28 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	"hch@...radead.org" <hch@...radead.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	"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 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 ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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