From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>,
Parav Pandit <parav@nvidia.com>, Bob Liu <bob.liu@oracle.com>,
Christoph Hellwig <hch@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
viro@zeniv.linux.org.uk, Jens Axboe <axboe@kernel.dk>,
bcrl@kvack.org, Jonathan Corbet <corbet@lwn.net>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC v4 10/11] vduse: Introduce a workqueue for irq injection
Date: Mon, 8 Mar 2021 15:01:46 +0800 [thread overview]
Message-ID: <a3ee164e-4de8-2305-ec4e-6eeef4aced29@redhat.com> (raw)
In-Reply-To: <CACycT3sZD2DEU=JxM-T+6dHBdsX5gOfAghh=Kg4PVw0PkNzEGw@mail.gmail.com>
On 2021/3/8 12:50 下午, Yongji Xie wrote:
> On Mon, Mar 8, 2021 at 11:04 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On 2021/3/5 4:12 下午, Yongji Xie wrote:
>>> On Fri, Mar 5, 2021 at 3:37 PM Jason Wang <jasowang@redhat.com> wrote:
>>>> On 2021/3/5 3:27 下午, Yongji Xie wrote:
>>>>> On Fri, Mar 5, 2021 at 3:01 PM Jason Wang <jasowang@redhat.com> wrote:
>>>>>> On 2021/3/5 2:36 下午, Yongji Xie wrote:
>>>>>>> On Fri, Mar 5, 2021 at 11:42 AM Jason Wang <jasowang@redhat.com> wrote:
>>>>>>>> On 2021/3/5 11:30 上午, Yongji Xie wrote:
>>>>>>>>> On Fri, Mar 5, 2021 at 11:05 AM Jason Wang <jasowang@redhat.com> wrote:
>>>>>>>>>> On 2021/3/4 4:58 下午, Yongji Xie wrote:
>>>>>>>>>>> On Thu, Mar 4, 2021 at 2:59 PM Jason Wang <jasowang@redhat.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?
>>>>>>>>>>
>>>>>>>>> After userspace call virtqueue_push(), it always call virtio_notify()
>>>>>>>>> immediately. In traditional VM (vhost-vdpa) cases, virtio_notify()
>>>>>>>>> will inject an irq to VM and return, then vcpu thread will call
>>>>>>>>> interrupt handler. But in container (virtio-vdpa) cases,
>>>>>>>>> virtio_notify() will call interrupt handler directly. So it looks like
>>>>>>>>> we have to optimize the virtio-vdpa cases. But one problem is we don't
>>>>>>>>> know whether we are in the VM user case or container user case.
>>>>>>>> Yes, but I still don't get why used ring is empty after the ioctl()?
>>>>>>>> Used ring does not use bounce page so it should be visible to the kernel
>>>>>>>> driver. What did I miss :) ?
>>>>>>>>
>>>>>>> Sorry, I'm not saying the kernel can't see the correct used vring. I
>>>>>>> mean the kernel will consume the used vring in the ioctl context
>>>>>>> directly in the virtio-vdpa case. In userspace's view, that means
>>>>>>> virtqueue_push() is used vring's producer and virtio_notify() is used
>>>>>>> vring's consumer. They will be called one by one in one thread rather
>>>>>>> than different threads, which looks odd and has a bad effect on
>>>>>>> performance.
>>>>>> Yes, that's why we need a workqueue (WQ_UNBOUND you used). Or do you
>>>>>> want to squash this patch into patch 8?
>>>>>>
>>>>>> So I think we can see obvious difference when virtio-vdpa is used.
>>>>>>
>>>>> But it looks like we don't need this workqueue in vhost-vdpa cases.
>>>>> Any suggestions?
>>>> I haven't had a deep thought. But I feel we can solve this by using the
>>>> irq bypass manager (or something similar). Then we don't need it to be
>>>> relayed via workqueue and vdpa. But I'm not sure how hard it will be.
>>>>
>>> Or let vdpa bus drivers give us some information?
>>
>> This kind of 'type' is proposed in the early RFC of vDPA series. One
>> issue is that at device level, we should not differ virtio from vhost,
>> so if we introduce that, it might encourge people to design a device
>> that is dedicated to vhost or virtio which might not be good.
>>
>> But we can re-visit this when necessary.
>>
> OK, I see. How about adding some information in ops.set_vq_cb()?
I'm not sure I get this, maybe you can explain a little bit more?
Thanks
>
> Thanks,
> Yongji
>
next prev parent reply other threads:[~2021-03-08 7:02 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 11:50 [RFC v4 00/11] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-02-23 11:50 ` [RFC v4 01/11] eventfd: Increase the recursion depth of eventfd_signal() Xie Yongji
2021-03-02 6:44 ` Jason Wang
2021-03-02 10:32 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 02/11] vhost-vdpa: protect concurrent access to vhost device iotlb Xie Yongji
2021-03-02 6:47 ` Jason Wang
2021-03-02 10:20 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 03/11] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-03-02 6:49 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 04/11] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-03-02 6:50 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 05/11] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-03-03 10:52 ` Mika Penttilä
2021-03-03 12:45 ` Yongji Xie
2021-03-03 13:38 ` Mika Penttilä
2021-03-04 3:07 ` Jason Wang
2021-03-04 5:40 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 06/11] vduse: Implement an MMU-based IOMMU driver Xie Yongji
2021-03-04 4:20 ` Jason Wang
2021-03-04 5:12 ` Yongji Xie
2021-03-05 3:35 ` Jason Wang
2021-03-05 6:15 ` Yongji Xie
[not found] ` <4db35f8c-ee3a-90fb-8d14-5d6014b4f6fa@redhat.com>
2021-03-05 7:13 ` Yongji Xie
2021-03-05 7:27 ` Jason Wang
2021-03-05 7:59 ` Yongji Xie
2021-03-08 3:17 ` Jason Wang
2021-03-08 3:45 ` Yongji Xie
2021-03-08 3:52 ` Jason Wang
2021-03-08 5:05 ` Yongji Xie
2021-03-08 7:04 ` Jason Wang
2021-03-08 7:08 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 07/11] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-03-04 6:27 ` Jason Wang
2021-03-04 8:05 ` Yongji Xie
2021-03-05 3:20 ` Jason Wang
2021-03-05 3:49 ` Yongji Xie
2021-03-10 12:58 ` Jason Wang
2021-03-11 2:28 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 08/11] vduse: Add config interrupt support Xie Yongji
2021-02-23 11:50 ` [RFC v4 09/11] Documentation: Add documentation for VDUSE Xie Yongji
2021-03-04 6:39 ` Jason Wang
2021-03-04 10:35 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 10/11] vduse: Introduce a workqueue for irq injection Xie Yongji
2021-03-04 6:59 ` Jason Wang
2021-03-04 8:58 ` Yongji Xie
2021-03-05 3:04 ` Jason Wang
2021-03-05 3:30 ` Yongji Xie
2021-03-05 3:42 ` Jason Wang
2021-03-05 6:36 ` Yongji Xie
2021-03-05 7:01 ` Jason Wang
2021-03-05 7:27 ` Yongji Xie
2021-03-05 7:36 ` Jason Wang
2021-03-05 8:12 ` Yongji Xie
2021-03-08 3:04 ` Jason Wang
2021-03-08 4:50 ` Yongji Xie
2021-03-08 7:01 ` Jason Wang [this message]
2021-03-08 7:16 ` Yongji Xie
2021-03-08 7:29 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 11/11] vduse: Support binding irq to the specified cpu Xie Yongji
2021-03-04 7:30 ` Jason Wang
2021-03-04 8:19 ` Yongji Xie
2021-03-05 3:11 ` Jason Wang
2021-03-05 3:37 ` Yongji Xie
2021-03-05 3:44 ` Jason Wang
2021-03-05 6:40 ` Yongji Xie
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