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    SubjectRe: Promise SX8 performance issues and CARM_MAX_Q
    Bernard Blackham wrote:
    > Hi,
    >
    > Playing with a recently acquired Promise SX8 card, we've found
    > similar performance results to Matt's post to lkml a few months back
    > at http://marc.theaimsgroup.com/?l=linux-kernel&m=110175890323356&w=2
    >
    > It appears that the driver is only submitting one command at a time
    > per port, which is at least one cause of the slowdowns. By raising
    > CARM_MAX_Q from 1 to 3 in drivers/block/sx8.c (it was 3 in an
    > earlier pre-merge incarnation of carmel.c), we're getting very
    > notable speed improvements, with no side effects just yet.
    >
    > Knowing very little about what this change has actually done, I've a
    > few questions:
    >
    > - Should this be considered dangerous?
    > - Why was it taken from 3 to 1?
    > - Is CARM_MAX_Q a number defined (or limited) by the hardware?

    In multi-port stress tests, we couldn't get SX8 to function reliably
    without locking up or corrupting data, with more than one outstanding
    command.

    Maybe a new firmware has solved this by now.

    Jeff



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