Re: [PATCH 6/6] net/vhost: perform SW checksum in Tx path

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Wenwu,

Sorry, I missed your review.

On 5/7/22 05:20, Ma, WenwuX wrote:
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: 2022年5月5日 18:27
>> To: dev@dpdk.org; jasowang@redhat.com; Xia, Chenbo
>> <chenbo.xia@intel.com>; david.marchand@redhat.com;
>> olivier.matz@6wind.com
>> Cc: stable@dpdk.org; Maxime Coquelin <maxime.coquelin@redhat.com>
>> Subject: [PATCH 6/6] net/vhost: perform SW checksum in Tx path
>>
>> Virtio specification supports guest checksum offloading for L4, which is
>> enabled with VIRTIO_NET_F_GUEST_CSUM feature negotiation. However,
>> the Vhost PMD does not advertise Tx checksum offload capabilities.
>>
>> Advertising these offload capabilities at the ethdev level is not enough,
>> because we could still end-up with the application enabling these offloads
>> while the guest not negotiating it.
>>
>> This patch advertizes the Tx checksum offload capabilities, and introduces a
>> compatibility layer to cover the case VIRTIO_NET_F_GUEST_CSUM has not
>> been negotiated but the application does configure the Tx checksum
>> offloads. This function performs the L4 Tx checksum in SW for UDP and TCP.
>> Compared to Rx SW checksum, the Tx SW checksum function needs to
>> compute the pseudo-header checksum, as we cannot knwo whether it was
>> done before.
>>
>> This patch does not advertize SCTP checksum offloading capability for now,
>> but it could be handled later if the need arises.
> 
> In virtio_enqueue_offload(), if RTE_MBUF_F_TX_IP_CKSUM is set, we will
> performs the L3 Tx checksum, why do not we advertise IPV4 checksum offloading capability?
> Will we advertise it later?
> 

Indeed, we have an IPv4 SW checksum fallback in Vhost library.
We could think about adding the capability, but that's not urgent I
think. Do you have a use-case where it is needed?

Regards,
Maxime