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

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Date:   Wed, 7 Dec 2016 17:44:14 -0500
From:   Keith Busch <keith.busch@...el.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Jens Axboe <axboe@...com>, linux-nvme@...ts.infradead.org,
        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 07, 2016 at 05:03:48PM -0500, Dan Streetman wrote:
> Change each queue's cq_vector to match its qid, instead of qid - 1.
> 
> The first queue is always the admin queue, and the remaining queues are
> I/O queues.  The interrupt vectors they use are all in the same array,
> however, the vector indexes for the admin and I/O queues are setup
> differently; the admin queue's cq_vector is manually set to 0, while
> each I/O queue's cq_vector is set to qid - 1.  Since the admin queue
> is qid 0, and the I/O queues start at qid 1, using qid - 1 is wrong for the
> I/O queues, as it makes the first I/O queue (qid 1) share the vector from
> the admin queue (qid 0), and no queue uses the last interrupt vector.
> Instead, each I/O queue should set their cq_vector to qid.

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.