Re: [Patch] SCSI I/O statistics

[Mike Christie <michaelc@cs.wisc.edu>]

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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