• Christoph Hellwig's avatar
    blk-mq: don't redistribute hardware queues on a CPU hotplug event · 4e68a011
    Christoph Hellwig authored
    Currently blk-mq will totally remap hardware context when a CPU hotplug
    even happened, which causes major havoc for drivers, as they are never
    told about this remapping.  E.g. any carefully sorted out CPU affinity
    will just be completely messed up.
    
    The rebuild also doesn't really help for the common case of cpu
    hotplug, which is soft onlining / offlining of cpus - in this case we
    should just leave the queue and irq mapping as is.  If it actually
    worked it would have helped in the case of physical cpu hotplug,
    although for that we'd need a way to actually notify the driver.
    Note that drivers may already be able to accommodate such a topology
    change on their own, e.g. using the reset_controller sysfs file in NVMe
    will cause the driver to get things right for this case.
    
    With the rebuild removed we will simplify retain the queue mapping for
    a soft offlined CPU that will work when it comes back online, and will
    map any newly onlined CPU to queue 0 until the driver initiates
    a rebuild of the queue map.
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarKeith Busch <keith.busch@intel.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    4e68a011
blk-mq.c 58.2 KB