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

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Message-ID: <2d3418d9-856c-37ee-7614-af5b721becd7@redhat.com>
Date:   Fri, 5 Mar 2021 11:04:42 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.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: [RFC v4 10/11] vduse: Introduce a workqueue for irq injection


On 2021/3/4 4:58 下午, Yongji Xie wrote:
> 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.


I'm not sure I get the issue.

THe used ring should be filled by virtqueue_push() which is done by 
userspace before?

Thanks


>
> Thanks,
> Yongji
>