Message-ID: <45199F92.106@cs.wisc.edu>
Date: Tue, 26 Sep 2006 16:45:54 -0500
From: Mike Christie <michaelc@cs.wisc.edu>
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To: Matthew Wilcox <matthew@wil.cx>
CC: Andrew Morton <akpm@osdl.org>, Martin Peschke <mp3@de.ibm.com>,
       linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [Patch] SCSI I/O statistics
References: <1159286194.2925.5.camel@dyn-9-152-230-71.boeblingen.de.ibm.com> <20060926103930.471b75a5.akpm@osdl.org> <20060926182347.GH5017@parisc-linux.org>
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Matthew Wilcox wrote:
> On Tue, Sep 26, 2006 at 10:39:30AM -0700, Andrew Morton wrote:
>> - Should it have been done at the block layer rather than at the scsi layer?
> 
> This was already mentioned when he sent it to linux-scsi a few days ago.
> There are scsi commands which bypass the block layer, such as SG_IO, and


I do not think any command completely bypasses the block layer now.
SG_IO, tape, sd and scanning insertion go through blk_execute_rq_nowait
for insertion. For completion they go through blk_complete_request +
end_that_request_first/last in the normal path and blk_complete_request
+ blk_requeue_request in the retry path.


> block layer stats can make an extremely busy disc look not busy.
> -
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