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From: David Ahern <dsahern@kernel.org>
To: Jesper Dangaard Brouer <jbrouer@redhat.com>,
	Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>,
	xdp-newbies@vger.kernel.org, cloud@xdp-project.net
Cc: brouer@redhat.com, Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
	Anton Protopopov <aspsk@isovalent.com>,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>,
	Jason Wang <jasowang@redhat.com>,
	"Karlsson, Magnus" <magnus.karlsson@intel.com>
Subject: [xdp-cloud] Re: Questions about Offloads and XDP-Hints regarding a Cloud-Provider Use-Case
Date: Wed, 28 Sep 2022 12:32:01 -0600	[thread overview]
Message-ID: <2d2d13bd-da93-2e04-3fd1-a5fd4713d7df@kernel.org> (raw)
In-Reply-To: <b207f828-8ba2-7bdd-01e6-3354172531b5@redhat.com>

On 9/28/22 11:07 AM, Jesper Dangaard Brouer wrote:
> 
> On 28/09/2022 15.54, Marcus Wichelmann wrote:
>>
>> I'm working for a cloud hosting provider and we're working on a new
>> XDP-based networking stack for our VM-Hosts that uses XDP to
>> accelerate the connectivity of our qemu/KVM VMs to the outside.
>>
> 
> Welcome to the community! Sounds like an excellent use-case and
> opportunity for speeding up the RX packets from physical NIC into the
> VM.  Good to hear someone (again) having this use-case. I've personally

+1

> not been focused on this use-case lately, mostly because community
> members that I was interacting with changed jobs, away from cloud
> hosting companies. Good to have a user back in this area!
> 
> 
>> For this, we use XDP_REDIRECT to forward packets between the physical
>> host NIC and the VM tap devices. The main issue we have now is, that
>> our VM guests have some virtio NIC offloads enabled: rx/tx
>> checksumming, TSO/GSO, GRO and Scatter-Gather.
> 
> Supporting RX-checksumming is part of the plans for XDP-hints, although
> virtio_net is not part of my initial patchset.

Lorenzo and I both had versions of a patch to propagate rx csum
validation to the VM on xdp redirect. I do not recall a version after
this one:

https://lore.kernel.org/netdev/cover.1622222367.git.lorenzo@kernel.org/

and I lost of track of what change is needed for it to go in.

> 
> XDP-redirect with GRO and Scatter-Gather frames are part of the
> multi-buff effort (Cc Lorenzo), but currently XDP_REDIRECT with
> multi-buff is disabled (except for cpumap), because the lack of
> XDP-feature bits, meaning we cannot determine (in kernel) if receiving
> net_device supports multi-buff (Cc Kumar).
> 
>> Currently, these offloads (especially TSO/GSO) are incompatible with
>> XDP_REDIRECT and result in packets being dropped. Because disabling
>> these offloads in all our customer VMs is not a good option, we're
>> searching for ways to support these offloads with XDP.
>>
> 
> To David Ahern, didn't the kernel recently loosen up on having to
> disable these offloads for KVM virtio_net?

not that I am aware. Still need tx offloads disabled.


This summarizes what I was looking into back in 2020, along with the
current state of XDP for VM use case:

https://legacy.netdevconf.info/0x14/pub/slides/24/netdev-0x14-XDP-and-the-cloud.pdf

source code is still on github too.

  reply	other threads:[~2022-09-28 18:32 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-28 13:54 [xdp-cloud] " Marcus Wichelmann
2022-09-28 18:07 ` [xdp-cloud] " Jesper Dangaard Brouer
2022-09-28 18:32   ` David Ahern [this message]
     [not found]     ` <YzTMmGuZjiO8+dVu@lore-desk>
2022-09-29  2:14       ` Jason Wang
2022-09-29  4:00         ` David Ahern
2022-09-29 13:16   ` Marcus Wichelmann
2022-10-03 10:56     ` Jesper Dangaard Brouer

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