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    SubjectRe: [PATCH] reworked IDE/general tagged command queueing
    On Wed, May 01 2002, Linus Torvalds wrote:
    > On Wed, 1 May 2002, Jens Axboe wrote:
    > >
    > > I've rewritten parts of the IDE TCQ stuff to be, well, a lot better in
    > > my oppinion. I had to accept that the ata_request and rq->special usage
    > > sucked, it was just one big mess.
    > Looks good.
    > I would have one more comment - it would be wonderful if somebody else who
    > was using tagged commands were to try to use this interface too, just to
    > verify that it doesn't have any major problems.
    > I'll be happy to merge the generic tag stuff even without that (on the
    > assumption that whatever deficiencies can be fixed later anyway), but it
    > would be wonderful to have some kind of validation of the genericity.
    > In particular, on an IDE TCQ device we expect the queue depth to be fixed,
    > but the SCSI subsystem considers queue depth to be only approximate
    > (because the drive internally might split a command or something, I don't
    > know). So I wonder how well this interface would interact with the
    > QUEUE_FULL handling that the SCSI layer does.
    > Maybe it doesn't matter, and maybe some blk_queue_invalidate_tags() magic
    > could do the right thing, but I'd like to get some kind of idea of whether
    > others can use it well..
    > (If not the SCSI layer, maybe somebody could look at DAC960 or cciss and
    > see whether they would seem to like the tag interface).

    Yeah, that's why I said the interface was simple on purpose right now.
    I'm sure it's extendable for some sort of adaptive queueing as well, I
    will try to provide some examples for that. cciss will eat a lot more
    commands than you think, it typically has a bigger internal queue depth
    than the block layer :-). If not dac960, then SCSI is a possibility.

    Jens Axboe

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