linux-kernel - Re: [PATCH 0/3] blk-mq & nvme: introduce .map

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Date:	Tue, 29 Sep 2015 22:45:47 +0000 (UTC)
From:	Keith Busch <keith.busch@...el.com>
To:	Ming Lei <tom.leiming@...il.com>
cc:	Jens Axboe <axboe@...nel.dk>, Keith Busch <keith.busch@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-nvme <linux-nvme@...ts.infradead.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 0/3] blk-mq & nvme: introduce .map_changed

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
> 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?
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