linux-kernel - Re: Virtio-scsi multiqueue irq affinity

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Message-ID: <87r1ifkoq5.ffs@nanos.tec.linutronix.de>
Date:   Mon, 10 May 2021 09:54:58 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "liaochang \(A\)" <liaochang1@...wei.com>,
        xuyihang <xuyihang@...wei.com>, Ming Lei <ming.lei@...hat.com>
Cc:     Peter Xu <peterx@...hat.com>, Christoph Hellwig <hch@....de>,
        Jason Wang <jasowang@...hat.com>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, minlei@...hat.com
Subject: Re: Virtio-scsi multiqueue irq affinity

Liao,

On Mon, May 10 2021 at 11:19, liaochang wrote:
> 1.We have a machine with 36 CPUs,and assign several RT threads to last
> two CPUs(CPU-34, CPU-35).

Which kind of machine? x86?

> 2.I/O device driver create single managed irq, the affinity of which
> includes CPU-34 and CPU-35.

If that driver creates only a single managed interrupt, then the
possible affinity of that interrupt spawns CPUs 0 - 35.

That's expected, but what is the effective affinity of that interrupt?

# cat /proc/irq/$N/effective_affinity

Also please provide the full output of

# cat /proc/interrupts

and point out which device we are talking about.

Thanks,

        tglx