Re: [PATCH 0/3] blk-mq & nvme: introduce .map_changed

From: Keith Busch
Date: Tue Sep 29 2015 - 18:45:56 EST

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.

- block core has to get the irq vector information which has to be
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?
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