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    SubjectRe: [PATCH 0/3] blk-mq & nvme: introduce .map_changed
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    On Wed, Sep 30, 2015 at 6:45 AM, Keith Busch <keith.busch@intel.com> wrote:
    > On Tue, 29 Sep 2015, Ming Lei wrote:
    >>
    >> Yes, I thought of that before, but it has the following cons:
    >>
    >> - some drivers/devices may need different IRQ affinity policy, such as
    >> virtio
    >> devices which has its own set affinity handler(see
    >> virtqueue_set_affinity()),
    >
    >
    > That's not a very good example to support your cause; virtio_scsi's use
    > is a perfect example for one that would benefit from letting blk-mq
    > handle affinity. virtio_scsi sets affinity only when there is a 1:1
    > mapping of cpu's to queue's, but this driver doesn't know the mapping
    > that blk-mq used, creating a potentially less than optimal mapping.

    The 1:1 mapping is introduced before blk-mq, and that doesn't mean we
    have to do that for blk-mq.

    Actualy I mean virtio-scsi just lets the 1st CPU of the cpumask handle
    the virt-queue's irq, instead of all CPUs mapped to the hw queue(virt-queue).

    >
    >> - block core has to get the irq vector information which has to be
    >> setup/finalized
    >> before blk-mq uses that for setting irq affinity, for example, in case
    >> NVMe's admin
    >> queue, its vector can be changed after admin queue's initialization.
    >
    >
    > Why do you want to put a hint on the admin queue's irq?

    No, I don't want, and it is just a example, I mean other drivers/devices
    may have this kind of situation too.

    --
    Ming Lei


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