Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

[Jason Wang]

On 2021/1/5 下午8:42, Xuan Zhuo wrote:
> On Tue, 5 Jan 2021 17:32:19 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> On 2021/1/5 下午5:11, Xuan Zhuo wrote:
>>> The first patch made some adjustments to xsk.
>>
>> Thanks a lot for the work. It's rather interesting.
>>
>>
>>> The second patch itself can be used as an independent patch to solve the problem
>>> that XDP may fail to load when the number of queues is insufficient.
>>
>> It would be better to send this as a separated patch. Several people
>> asked for this before.
>>
>>
>>> The third to last patch implements support for xsk in virtio-net.
>>>
>>> A practical problem with virtio is that tx interrupts are not very reliable.
>>> There will always be some missing or delayed tx interrupts. So I specially added
>>> a point timer to solve this problem. Of course, considering performance issues,
>>> The timer only triggers when the ring of the network card is full.
>>
>> This is sub-optimal. We need figure out the root cause. We don't meet
>> such issue before.
>>
>> Several questions:
>>
>> - is tx interrupt enabled?
>> - can you still see the issue if you disable event index?
>> - what's backend did you use? qemu or vhost(user)?
> Sorry, it may just be a problem with the backend I used here. I just tested the
> latest qemu and it did not have this problem. I think I should delete the
> timer-related code?


Yes, please.


>
>>
>>> Regarding the issue of virtio-net supporting xsk's zero copy rx, I am also
>>> developing it, but I found that the modification may be relatively large, so I
>>> consider this patch set to be separated from the code related to xsk zero copy
>>> rx.
>>
>> That's fine, but a question here.
>>
>> How is the multieuque being handled here. I'm asking since there's no
>> programmable filters/directors support in virtio spec now.
>>
>> Thanks
> I don't really understand what you mean. In the case of multiple queues,
> there is no problem.


So consider we bind xsk to queue 4, how can you make sure the traffic to 
be directed queue 4? One possible solution is to use filters as what 
suggested in af_xdp.rst:

       ethtool -N p3p2 rx-flow-hash udp4 fn
       ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
           action 16
...

But virtio-net doesn't have any filters that could be programmed from 
the driver.

Anything I missed here?

Thanks


>
>>
>>> Xuan Zhuo (5):
>>>     xsk: support get page for drv
>>>     virtio-net: support XDP_TX when not more queues
>>>     virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx
>>>     xsk, virtio-net: prepare for support xsk
>>>     virtio-net, xsk: virtio-net support xsk zero copy tx
>>>
>>>    drivers/net/virtio_net.c    | 643 +++++++++++++++++++++++++++++++++++++++-----
>>>    include/linux/netdevice.h   |   1 +
>>>    include/net/xdp_sock_drv.h  |  10 +
>>>    include/net/xsk_buff_pool.h |   1 +
>>>    net/xdp/xsk_buff_pool.c     |  10 +-
>>>    5 files changed, 597 insertions(+), 68 deletions(-)
>>>
>>> --
>>> 1.8.3.1
>>>

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Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

[Jason Wang]

On 2021/1/6 上午10:55, Xuan Zhuo wrote:
> On Wed, 6 Jan 2021 10:46:43 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> On 2021/1/5 下午8:42, Xuan Zhuo wrote:
>>> On Tue, 5 Jan 2021 17:32:19 +0800, Jason Wang <jasowang@redhat.com> wrote:
>>>> On 2021/1/5 下午5:11, Xuan Zhuo wrote:
>>>>> The first patch made some adjustments to xsk.
>>>> Thanks a lot for the work. It's rather interesting.
>>>>
>>>>
>>>>> The second patch itself can be used as an independent patch to solve the problem
>>>>> that XDP may fail to load when the number of queues is insufficient.
>>>> It would be better to send this as a separated patch. Several people
>>>> asked for this before.
>>>>
>>>>
>>>>> The third to last patch implements support for xsk in virtio-net.
>>>>>
>>>>> A practical problem with virtio is that tx interrupts are not very reliable.
>>>>> There will always be some missing or delayed tx interrupts. So I specially added
>>>>> a point timer to solve this problem. Of course, considering performance issues,
>>>>> The timer only triggers when the ring of the network card is full.
>>>> This is sub-optimal. We need figure out the root cause. We don't meet
>>>> such issue before.
>>>>
>>>> Several questions:
>>>>
>>>> - is tx interrupt enabled?
>>>> - can you still see the issue if you disable event index?
>>>> - what's backend did you use? qemu or vhost(user)?
>>> Sorry, it may just be a problem with the backend I used here. I just tested the
>>> latest qemu and it did not have this problem. I think I should delete the
>>> timer-related code?
>>
>> Yes, please.
>>
>>
>>>>> Regarding the issue of virtio-net supporting xsk's zero copy rx, I am also
>>>>> developing it, but I found that the modification may be relatively large, so I
>>>>> consider this patch set to be separated from the code related to xsk zero copy
>>>>> rx.
>>>> That's fine, but a question here.
>>>>
>>>> How is the multieuque being handled here. I'm asking since there's no
>>>> programmable filters/directors support in virtio spec now.
>>>>
>>>> Thanks
>>> I don't really understand what you mean. In the case of multiple queues,
>>> there is no problem.
>>
>> So consider we bind xsk to queue 4, how can you make sure the traffic to
>> be directed queue 4? One possible solution is to use filters as what
>> suggested in af_xdp.rst:
>>
>>         ethtool -N p3p2 rx-flow-hash udp4 fn
>>         ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
>>             action 16
>> ...
>>
>> But virtio-net doesn't have any filters that could be programmed from
>> the driver.
>>
>> Anything I missed here?
>>
>> Thanks
> I understand what you mean, this problem does exist, and I encountered it when I
> tested qemu.
>
> First of all, this is that the problem only affects recv. This patch is for
> xmit. Of course, our normal business must also have recv scenarios.
>
> My solution in developing the upper-level application is to bond all the queues
> to ensure that we can receive the packets we want.


I'm not sure I get you here. Note that. one advantage of AF_XDP is that 
is allows XSK to be bound to a specific queue and the rest could still 
be used by kernel.


>   And I think in the
> implementation of the use, even if the network card supports filters, we should
> also bond all the queues, because we don't know which queue the traffic we care
> about will arrive from.


With the help of filters the card can select a specific queue based on 
hash or n-tuple so it should work?


>
> Regarding the problem of virtio-net, I think our core question is whether we
> need to deal with this problem in the driver of virtio-net, I personally think
> that we should add the virtio specification to define this scenario.


Yes, so do you want to do that? It would make virtio-net more user 
friendly to AF_XDP. (Or if you wish I can post patch to extend the spec).


>
> When I tested it, I found that some cloud vendors' implementations guarantee
> this queue selection algorithm.


Right, though spec suggest a automatic steering algorithm but it's not 
mandatory. Vendor can implement their own.

But hash or ntuple filter should be still useful.

Thanks


>
> Thanks!!
>
>>
>>>>> Xuan Zhuo (5):
>>>>>      xsk: support get page for drv
>>>>>      virtio-net: support XDP_TX when not more queues
>>>>>      virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx
>>>>>      xsk, virtio-net: prepare for support xsk
>>>>>      virtio-net, xsk: virtio-net support xsk zero copy tx
>>>>>
>>>>>     drivers/net/virtio_net.c    | 643 +++++++++++++++++++++++++++++++++++++++-----
>>>>>     include/linux/netdevice.h   |   1 +
>>>>>     include/net/xdp_sock_drv.h  |  10 +
>>>>>     include/net/xsk_buff_pool.h |   1 +
>>>>>     net/xdp/xsk_buff_pool.c     |  10 +-
>>>>>     5 files changed, 597 insertions(+), 68 deletions(-)
>>>>>
>>>>> --
>>>>> 1.8.3.1
>>>>>

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Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

[Michael S. Tsirkin]

On Tue, Jan 05, 2021 at 05:11:38PM +0800, Xuan Zhuo wrote:
> The first patch made some adjustments to xsk.
> 
> The second patch itself can be used as an independent patch to solve the problem
> that XDP may fail to load when the number of queues is insufficient.
> 
> The third to last patch implements support for xsk in virtio-net.
> 
> A practical problem with virtio is that tx interrupts are not very reliable.
> There will always be some missing or delayed tx interrupts.

Would appreciate a bit more data on this one. Is this a host bug? Device bug?
Can we limit the work around somehow?

> So I specially added
> a point timer to solve this problem. Of course, considering performance issues,
> The timer only triggers when the ring of the network card is full.
> 
> Regarding the issue of virtio-net supporting xsk's zero copy rx, I am also
> developing it, but I found that the modification may be relatively large, so I
> consider this patch set to be separated from the code related to xsk zero copy
> rx.
> 
> Xuan Zhuo (5):
>   xsk: support get page for drv
>   virtio-net: support XDP_TX when not more queues
>   virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx
>   xsk, virtio-net: prepare for support xsk
>   virtio-net, xsk: virtio-net support xsk zero copy tx
> 
>  drivers/net/virtio_net.c    | 643 +++++++++++++++++++++++++++++++++++++++-----
>  include/linux/netdevice.h   |   1 +
>  include/net/xdp_sock_drv.h  |  10 +
>  include/net/xsk_buff_pool.h |   1 +
>  net/xdp/xsk_buff_pool.c     |  10 +-
>  5 files changed, 597 insertions(+), 68 deletions(-)
> 
> --
> 1.8.3.1

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Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

[Jason Wang]

On 2021/1/5 下午5:11, Xuan Zhuo wrote:
> The first patch made some adjustments to xsk.


Thanks a lot for the work. It's rather interesting.


>
> The second patch itself can be used as an independent patch to solve the problem
> that XDP may fail to load when the number of queues is insufficient.


It would be better to send this as a separated patch. Several people 
asked for this before.


>
> The third to last patch implements support for xsk in virtio-net.
>
> A practical problem with virtio is that tx interrupts are not very reliable.
> There will always be some missing or delayed tx interrupts. So I specially added
> a point timer to solve this problem. Of course, considering performance issues,
> The timer only triggers when the ring of the network card is full.


This is sub-optimal. We need figure out the root cause. We don't meet 
such issue before.

Several questions:

- is tx interrupt enabled?
- can you still see the issue if you disable event index?
- what's backend did you use? qemu or vhost(user)?


>
> Regarding the issue of virtio-net supporting xsk's zero copy rx, I am also
> developing it, but I found that the modification may be relatively large, so I
> consider this patch set to be separated from the code related to xsk zero copy
> rx.


That's fine, but a question here.

How is the multieuque being handled here. I'm asking since there's no 
programmable filters/directors support in virtio spec now.

Thanks


>
> Xuan Zhuo (5):
>    xsk: support get page for drv
>    virtio-net: support XDP_TX when not more queues
>    virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx
>    xsk, virtio-net: prepare for support xsk
>    virtio-net, xsk: virtio-net support xsk zero copy tx
>
>   drivers/net/virtio_net.c    | 643 +++++++++++++++++++++++++++++++++++++++-----
>   include/linux/netdevice.h   |   1 +
>   include/net/xdp_sock_drv.h  |  10 +
>   include/net/xsk_buff_pool.h |   1 +
>   net/xdp/xsk_buff_pool.c     |  10 +-
>   5 files changed, 597 insertions(+), 68 deletions(-)
>
> --
> 1.8.3.1
>

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