linux-kernel - RE: IRQ affinity problem from virtio

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Date:   Wed, 16 Nov 2022 11:54:35 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Angus Chen <angus.chen@...uarmicro.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ming Lei <ming.lei@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Subject: RE: IRQ affinity problem from virtio_blk

On Wed, Nov 16 2022 at 00:46, Angus Chen wrote:
>> On Wed, Nov 16 2022 at 00:04, Thomas Gleixner wrote:
>> >>> But then it also has another 79 vectors put aside for the other queues,
> en,it not the truth,in fact ,I just has one queue for one virtio_blk.

Which does not matter. See my reply to Michael. It's ONE vector per CPU
and block device.

> Nov 14 11:48:45 localhost kernel: virtio_blk virtio181: 1/0/0 default/read/poll queues
> Nov 14 11:48:45 localhost kernel: virtio_blk virtio181: [vdpr] 20480 512-byte logical blocks (10.5 MB/10.0 MiB)
> Nov 14 11:48:46 localhost kernel: virtio-pci 0000:37:16.4: enabling device (0000 -> 0002)
> Nov 14 11:48:46 localhost kernel: virtio-pci 0000:37:16.4: virtio_pci: leaving for legacy driver
> Nov 14 11:48:46 localhost kernel: virtio_blk virtio182: 1/0/0 default/read/poll queues---------the virtio182 means index 182.
> Nov 14 11:48:46 localhost kernel: vp_find_vqs_msix return err=-28-----------------------------the first time we get 'no space' error from irq subsystem. 

That's close to 200 virtio devices and the vector space is exhausted.
Works as expected.

Interrupt vectors are a limited resource on x86 and not only on x86. Not
any different from any other resource.

Thanks,

        tglx