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    SubjectSlow PPP, SCSI, and spinlocks
    Ok, this is really a follow up to my previous Slow PPP problem with my PS/2
    at home. I had originally traced this to the 2.1.102 patch where the
    cli/sti routines were converted to save_flags/restore_flags. Thanks to
    input from another user who pointed out that the most likely scenario here
    was that the cli/sti routine was inadvertenly renabling interrupts that had
    been disabled by other code I pushed further into my studies of the irq
    handling in Linux 2.2. Sure enough, the problem actually stems from the
    change to wrap the SCSI interrupts handlers with spinlocks, basically
    meaning that all interrupts remain disabled during the entire interrupt
    handling routine, and by sheer luck the IBM SCSI driver contained a cli/sti
    routine that reenabled interrupts causing my serial port to continue to
    function properly until 2.1.102 when the routine was replaced by

    I then tested this more completely by using the stock 2.2.1 IBM SCSI driver
    with only one change, I removed the spin_lock_irqsave/spin_lock_irqrestore
    from the do_interrupt_hanlder routine. With this minor change I no longer
    loose serial interrupts.

    The most information I could find about this change was in Linus' comments
    about the 2.1.95 patch, and by my limited interpretation the changes were
    mainly for SMP. So, my big question then is this, is it really neccessary
    to do spin_locks on SCSI interrupt handlers even on UP machines? So far
    I've noticed no ill effects with my change.

    The problem with this seems to occur on machines other than mine. I
    received several emails from other users who were experiencing similar
    trouble with the Seagte scsi driver.

    I'd like to hear some other comments on this. Perhaps there are better ways
    to handle this such as trimming down the interrupt handler and moving some
    portions to another routine that will funtion with interrupts enabled.

    Any help would be greatly appreciated.


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