netdev - Re: Re: [RFC v4 10/11] vduse: Introduce a workqueue for irq injection

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Message-ID: <CACycT3tqM=ALOG1r0Ve6UTGmwJ7Wg7fQpLZypjZsJF1mJ+adMA@mail.gmail.com>
Date:   Thu, 4 Mar 2021 16:58:27 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>, Bob Liu <bob.liu@...cle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: Re: [RFC v4 10/11] vduse: Introduce a workqueue for irq injection

On Thu, Mar 4, 2021 at 2:59 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2021/2/23 7:50 下午, Xie Yongji wrote:
> > This patch introduces a workqueue to support injecting
> > virtqueue's interrupt asynchronously. This is mainly
> > for performance considerations which makes sure the push()
> > and pop() for used vring can be asynchronous.
>
>
> Do you have pref numbers for this patch?
>

No, I can do some tests for it if needed.

Another problem is the VIRTIO_RING_F_EVENT_IDX feature will be useless
if we call irq callback in ioctl context. Something like:

virtqueue_push();
virtio_notify();
    ioctl()
-------------------------------------------------
        irq_cb()
            virtqueue_get_buf()

The used vring is always empty each time we call virtqueue_push() in
userspace. Not sure if it is what we expected.

Thanks,
Yongji