Re: Netvsc PMD : Hotplug handling : checksum offloads

[Nandini Rangaswamy <nandini.rangaswamy@broadcom.com>]

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Hi Stephen,
I am testing UDP IPv4 offloads. Earlier with failsafe PMD , my dpdk app
would subscribe to hotplug add and delete callbacks. In Hotplug add
callback the appropriate mbuf flags were set for hardware to perform
checksum offload and in hotplug delete, the function pointer was modified
to calculate checksum in software.
To test netvsc PMD, I have commented out the code in hotplug callbacks to
understand what happens. As you mentioned, as part of hotplug add,
hn_vf_add restores all the VF offloads and it works as expected. In case of
hotplug removal, I notice that even in the absence of software checksum ,
the packets are reaching the destination with the correct checksum. The
dpdk app continues to set mbuf flags for offload in the sender. I expected
packets to be dropped at the sender because offloads should be absent as VF
is removed. Does netvsc pmd calculate checksum if mbuf checksum offload
flags are set and VF is absent?

Regards,
Nandini

On Thu, Oct 24, 2024 at 2:38 PM Nandini Rangaswamy <
nandini.rangaswamy@broadcom.com> wrote:

> Hi Stephen/Long,
> I did some more code instrumentation and I observed that when a hotplug
> add event is received, the conf is applied back to VF and offloads work as
> expected.
> I also observe that when VF is removed, the offloads still continue to
> work as expected. Is this because the offloads are not unset when VF is
> removed ?
> Regards,
> Nandini
>
> On Thu, Oct 24, 2024 at 9:33 AM Stephen Hemminger <
> stephen@networkplumber.org> wrote:
>
>> On Wed, 23 Oct 2024 13:34:53 -0700
>> Nandini Rangaswamy <nandini.rangaswamy@broadcom.com> wrote:
>>
>> > Hi Stephen,
>> > The code looking at checksum flags in each packet would not give us
>> desired
>> > performance. Instead, should the dpdk app register callbacks for hotplug
>> > add and re-configure the checksum offloads when VF is added again?
>> > Regards,
>> > Nandini
>>
>> The code in hn_vf_add which is where netvsc PMD handles hot add of VF
>> should be feeding the current offload settings to the VF.
>>
>> Maybe the rte_eth_conf being passed to VF is incorrect, or
>> the configuration step there is failing. Probably need more
>> instrumentation
>> and logs to tell.
>>
>

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