[virtio-comment] Re: [virtio-dev] Re: [virtio-comment] [PATCH] virtio-net: support per-queue coalescing moderation

[Heng Qi <hengqi@linux.alibaba.com>]

在 2023/2/9 上午6:35, Alvaro Karsz 写道:
>>> From: Alvaro Karsz <alvaro.karsz@solid-run.com>
>>> Sent: Wednesday, February 8, 2023 4:56 PM
>>>> Alvaro,
>>>> Do you know if any software used it? Can you get some real data?
>>> I implemented this feature in our DPU, so at least 1 vendor is using this feature
>> But which software (virtio net driver) in which OS is using this?
> Sorry, I'm not sure I understand your question.
>
> The feature is implemented in the linux kernel
> https://github.com/torvalds/linux/commit/699b045a8e43bd1063db4795be685bfd659649dc
> So we'll always have kernel versions accepting this feature, if offered.
>
>>> (I will add support for the per vq command of course).
>>> I really don't know about other vendors..
>>>
>>> You are suggesting to reserve the command and feature bit for safety, so, if we
>>> reserve them, why not just use them? What do we lose here?
>>>
>> If it is used by some unknown software, only that sw breaks by using non release spec.
>> If we use it by changing the definition, it may break that unknown sw.
>> If we know there is no known sw, we are better of with redefinition (by adding vqn, and by removing tx,rx from it).
>>
>>> Not having this feature/command even complicates things now that we are
>>> talking about removing the RX and TX from the per vq command, how do you
>>> change parameters to all TX queues? to all RX queues? we'll need 2 special
>>> indexes, so we now need le32 to hold the queue index.
>> No need for special index.
>> How does a driver disable all queues or reset all queues? -> One by one.
>> So if user want to change for all TXQ, sw can do it one by one by iterating TXQ vqns.
> Yes, but resetting the queues doesn't require a control command.
> If a server has 64K queues, and a user wants to set all coalescing
> parameters to X (maybe with ethtool), it will generate 64K control
> commands..

At least our hardware design doesn't expect that.

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