linux-kernel - Re: [PATCH] nvme: use the correct msix vector for each queue

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Date:   Wed, 7 Dec 2016 17:46:34 -0500
From:   Dan Streetman <ddstreet@...e.org>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Jens Axboe <axboe@...com>, linux-nvme@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dan Streetman <dan.streetman@...onical.com>
Subject: Re: [PATCH] nvme: use the correct msix vector for each queue

On Wed, Dec 7, 2016 at 5:49 PM, Keith Busch <keith.busch@...el.com> wrote:
> On Wed, Dec 07, 2016 at 05:36:00PM -0500, Dan Streetman wrote:
>> On Wed, Dec 7, 2016 at 5:44 PM, Keith Busch <keith.busch@...el.com> wrote:
>> > pci_alloc_irq_vectors doesn't know you intend to make the first
>> > vector special, so it's going to come up with a CPU affinity from
>> > blk_mq_pci_map_queues that clashes with what you've programmed in the
>> > IO completion queues.
>>
>> I don't follow.  You're saying you mean to share cq_vector 0 between
>> the admin queue and io queue 1?
>
> I'm just saying that blk-mq's hctx mapping will end up choosing a queue
> who's vector is mapped to a different CPU, and we don't want that.
>
> We are currently sharing the first IO queue's interrupt vector with
> the admin queue's on purpose. Are you saying there's something wrong
> with that?

that's intentional?  Ok then.  That's extremely non-obvious.

Is there a reason you want to share the interrupt between the queues?