Re: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] Re: [PATCH v7] virtio-net: support inner header hash

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

Any more discussions or comments? Please let me know if this is OK with you.
and the v8 version is released at
[1] https://lists.oasis-open.org/archives/virtio-dev/202302/msg00094.html

Thanks.

å 2023/2/9 äå5:57, Heng Qi åé:
> å 2023/2/9 äå1:34, Parav Pandit åé:
> > > From: Heng Qi <hengqi@linux.alibaba.com>
> > > Sent: Thursday, February 9, 2023 12:21 AM
> > > > > > > Thanks for your reply.
> > > > > > I had one last question. Why do we need to inform the
> > > > > hash_report_tunnel_type of the outer header in the virtio_net_hdr?
> > > > > > Is this for debug? Or is there a use case that will process this 
> > > > > > value?
> > > > > The driver may use it to do some statistical information, or do some
> > > > > rx classification based on the rx hash, and we'd better not hide
> > > > > information from the driver.
> > > > Statistical information is better gathered via stats, instead of 
> > > > adding such code
> > > in driver data path.
> > >
> > > A cautionary note : the source of hash_report_tunnel comes from the
> > > discussion here
> > > https://lists.oasis-open.org/archives/virtio-dev/202211/msg00063.html
> > > If I understand correctly, if virtio-net-hdr also has 
> > > hash_report_tunnel, how
> > > does the driver do statistics?
> > I am asking to avoid having hash_report_tunnel in virtio_net_hdr if 
> > it is only for the statistics purpose.
>
> Parav, I don't seem to follow this.
>
> Note that the hash_report(le16) and padding reserved(le16) fields only 
> exist when VIRTIO_NET_F_HASH_REPORT is negotiated,
> and hash_report_tunnel only uses the first 8 bits of padding_reserved, 
> which does not add any overhead.
>
> Whether to reuse hash_report or use the new hash_report_tunnel 
> initially has been discussed: 
> https://lists.oasis-open.org/archives/virtio-dev/202211/msg00065.html .
>
> > If it has more use than just statistics, I like to understand its use 
> > in rx packet processing flow, if there is any and to describe in 
> > commit log too.
>
> I think there are still some important points, such as the kernel or 
> driver forwards the packet,
> and the hash value is used when selecting the queue, but at this time 
> they want to know whether
> the hash value comes from the inner or outer header.
> What if it doesn't want to forward based on the hash calculated by the 
> inner header, but only uses the hash calculated by the outer header?
>
> Thanks.
>
> > Below [1] says about driver doing some rx classification. It is 
> > unclear on inner or outer.
> > The response is not very clear to me, about how this field is useful.
> >
> > [1] 
> > https://lists.oasis-open.org/archives/virtio-dev/202211/msg00063.html
> >
> > If driver needs to know the statistics of it, it can query them from 
> > the device by introducing statistics cmd.
>
>
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