Re: NVME is not using CPU0

[Yaroslav Isakov <yaroslav.isakov@gmail.com>]

Hello, Keith! I've tried to pin fio process's threads, but with no
luck. On my system, your command gave this:
0, 1
2
3
4
5
6
7
So, it looks like first queue should use two CPUs, but using only
CPU1. Oh, and if I'm run fio with 2 threads, without pinning, I can
see increasing numbers in /proc/interrupts for all CPUs besides CPU0

пн, 9 мар. 2020 г. в 02:55, Keith Busch <kbusch@kernel.org>:
>
> On Mon, Mar 09, 2020 at 12:46:24AM +0100, Yaroslav Isakov wrote:
> > Hello! I found that my nvme disk is not assigning any queue on CPU0. I
> > think, that maybe it could be a bug, related to admin queue. Function
> > queue_irq_offset return 1 with note that this is for admin queue. But
> > on my system, admin queue is on the same CPU as q2. Here is part of
> > /proc/interrupts
>
> All CPUs are assigned an nvme IO queue. Pin your IO process to CPU 0, it
> will function just fine. Another way to confirm is run:
>
>   # cat /sys/block/nvme0n1/mq/*/cpu_list
>
> Every CPU should be accounted for in the output.
>
> What you've observed is that your controller doesn't support enough IO
> queues or MSI vectors (or both) to assign to each CPU. It just means that
> a command you submit on the queue assigned to CPU 0 will get completed on
> a different CPU.

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