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    SubjectRe: [PATCH] Promise 'stex' driver
    On Thu, Jul 20 2006, Jeff Garzik wrote:
    > Jens Axboe wrote:
    > >On Thu, Jul 20 2006, Jeff Garzik wrote:
    > >>James Bottomley wrote:
    > >>>On Thu, 2006-07-20 at 17:27 -0400, Jeff Garzik wrote:
    > >>>>Since _no individual SCSI driver_ uses the block layer
    > >>>>tagging, it is likely that some instability and core kernel
    > >>>>development
    > >>>>will occur, in order to make that work.
    > >>>That's not quite true: 53c700 and tmscsim both use it ... I could with
    > >>>the usage were wider, but at least 53c700 has pretty regular and
    > >>>constant usage ... enough I think to validate the block tag code (it's
    > >>>been using it for the last three years).
    > >>Not for the case being discussed in this thread, adapter-wide tags.
    > >
    > >That just means the map is shared, otherwise there should be little if
    > >any difference.
    > >
    > >>AFAICS, no file in include/scsi/* or drivers/scsi/* ever calls
    > >>blk_queue_init_tags() with a non-NULL third arg.
    > >
    > >grpe again, it's in scsi_tcq.h.
    > What tree are you looking at?
    > There is only one user in the entire tree, and NULL is hardcoded as the
    > third arg. This is 2.6.18-rc2:

    Sorry, missed your non-NULL statement, I thought you meant in generel.

    As long as you get the locking right for the map access, there's really
    nothing that seperates shared vs non-shared tag mappings. So I don't
    think it's a big deal.

    If we don't encourage new drivers to use the block layer tagging, we
    might as well not bother with it.

    Jens Axboe

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