• Finn Thain's avatar
    ncr5380: Fix soft lockups · 0a4e3612
    Finn Thain authored
    Because of the rudimentary design of the chip, it is necessary to poll the
    SCSI bus signals during PIO and this tends to hog the CPU. The driver will
    accept new commands while others execute, and this causes a soft lockup
    because the workqueue item will not terminate until the issue queue is
    emptied.
    
    When exercising dmx3191d using sequential IO from dd, the driver is sent
    512 KiB WRITE commands and 128 KiB READs. For a PIO transfer, the rate is
    is only about 300 KiB/s, so these are long-running commands. And although
    PDMA may run at several MiB/s, interrupts are disabled for the duration
    of the transfer.
    
    Fix the unresponsiveness and soft lockup issues by calling cond_resched()
    after each command is completed and by limiting max_sectors for drivers
    that don't implement real DMA.
    Signed-off-by: default avatarFinn Thain <fthain@telegraphics.com.au>
    Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
    Tested-by: default avatarOndrej Zary <linux@rainbow-software.org>
    Tested-by: default avatarMichael Schmitz <schmitzmic@gmail.com>
    Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
    0a4e3612
dtc.c 11.9 KB