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    SubjectRe: [PATCH] queue barrier support


    On Wednesday, February 13, 2002 01:26:12 PM -0500 James Bottomley <James.Bottomley@steeleye.com> wrote:

    > axboe@suse.de said:
    >> ChangeSet@1.297, 2002-02-13 13:42:39+01:00, axboe@burns.home.kernel.dk
    >> Add support for SCSI drivers to indicate support for ordered tags
    >> http://bitmover.com:8888//tmp/v2_logging/athlon.transmeta.com/
    >> torvalds-2002020517305 \ 6-16047-c1d11a41ed024864/cset@1.133.114.4?nav=
    >> index.html|ChangeSet@-1h
    >
    >> ChangeSet@1.298, 2002-02-13 13:43:04+01:00, axboe@burns.home.kernel.dk
    >> Add ordered tag support to the aic7xxx scsi driver
    >
    > The rest of the aic7xxx code uses MSG_ORDERED_TASK rather than
    > MSG_ORDERED_Q_TAG. You have to scan through the headers to see that these are
    ># defined the same.

    Jens, my patch from yesterday has this fixed.

    >
    > A problem (that is probably only an issue for older drives) is that while
    > technically the standard requires all 3 types of TAG to be supported if tag
    > queueing is, some drives really only have simple tag support in their
    > firmware, so you may need to add a blacklist for ordered tags on certain
    > drives.

    Yes, this could get sticky. Does anyone know if other OSes have already
    done this?

    >
    > A further issue is that you haven't added anything to the error recovery code
    > for this. If error recovery is activated for the device at the reset level,
    > all tags will be discarded by the device. The eh will retry the failing
    > command and then the other tagged commands will be re-issued from the
    > scsi_bottom_half_handler (assuming the low level device driver immediately
    > fails them with DID_RESET) in the order in which the low level driver failed
    > them. Thus you have potentially completely messed up the ordering when the
    > commands all get retried.

    I was wondering about this, we would need to change the error handler to
    fail all the requests after the barrier. I was hoping the driver
    did this for us ;-)

    -chris

    -
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