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From:   =?UTF-8?B?5p2O6I+y?= <lifei.shirley@bytedance.com>
Date:   Mon, 22 Jul 2019 11:22:02 +0800
Message-ID: <CA+=e4K5rn7-avNT3e07dfXkh=ZO2+RvthjqW15gZv-uFYrCs3A@mail.gmail.com>
Subject: Re: [External Email] Re: [PATCH v1 0/2] virtio-mmio: support multiple
 interrupt vectors
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        virtio-dev@lists.oasis-open.org
Cc:     linux-kernel@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
        Pawel Moll <pawel.moll@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Fam Zheng <zhengfeiran@bytedance.com>
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On Fri, Jul 19, 2019 at 11:14 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Fri, Jul 19, 2019 at 09:31:33PM +0800, Fei Li wrote:
> > Hi,
> >
> > This patch series implements multiple interrupt vectors support for
> > virtio-mmio device. This is especially useful for multiqueue vhost-net
> > device when using firecracker micro-vms as the guest.
> >
> > Test result:
> > With 8 vcpus & 8 net queues set, one vhost-net device with 8 irqs can
> > receive 9 times more pps comparing with only one irq:
> > - 564830.38 rxpck/s for 8 irqs on
> > - 67665.06 rxpck/s for 1 irq on
> >
> > Please help to review, thanks!
> >
> > Have a nice day
> > Fei
>
>
> Interesting. The spec says though:
>
>         4.2.3.4
>         Notifications From The Device
>         The memory mapped virtio device is using a single, dedicated interrupt signal, which is asserted when at
>         least one of the bits described in the description of InterruptStatus is set. This is how the device sends a
>         used buffer notification or a configuration change notification to the device.
>
Yes, the spec needs to be updated if we want to use mult-irqs.
>
> So I'm guessing we need to change the host/guest interface?
Just to confirm, does the "the host/guest interface" you mentioned mean how to
pass the irq information from the user space tool to guest kernel?
In this patch, we do this by passing the [irq_start, irq_end]
interface via setting guest
kernel command line, that is done in vm_cmdline_set().
Also there is another way to do this: add two new registers describing irq info
(irq_start & irq_end OR irq_start & irq_numbers) to the virtio config space.

Which one do you prefer?

> If true pls cc virtio-dev.
Sure.
>
> Also, do we need to update dt bindings documentation?
You mean the following doc? Sure. :)
https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/virtio/mmio.txt

Thanks for the review!

Have a nice day
Fei


>
> >
> > Fam Zheng (1):
> >   virtio-mmio: Process vrings more proactively
> >
> > Fei Li (1):
> >   virtio-mmio: support multiple interrupt vectors
> >
> >  drivers/virtio/virtio_mmio.c | 238 +++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 196 insertions(+), 42 deletions(-)
> >
> > --
> > 2.11.0