Re: [PATCH net] selftests: drv-net: ping: Wait for carrier after toggling offloads

[Pin-yen Lin]

Hi Jakub,

Thanks for the review.

On Wed, Mar 18, 2026 at 5:28 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Tue, 17 Mar 2026 18:01:17 -0700 Pin-yen Lin wrote:
> > Toggling checksum offload (or HW-GRO via feature dependencies) can cause
> > certain physical interfaces to undergo a reset or a temporary link-down
> > state. In the ping.py test, this leads to immediate test failures if the
> > ping is attempted before the carrier is restored.
> >
> > This is observed when running the test with GVE driver when HW-GRO is
> > enabled. When checksum offload is toggled, HW-GRO is toggled as well
> > because of the feature dependency. This leads to an interface reset,
> > causing the subsequent ping to fail.
> >
> > Add a sleep period after changing these features to allow the link to
> > stabilize.
>
> Sounds like the test found a legitimate problem. The configuration
> should not return to user space until the operation has completed.
> User should not have to sleep 10sec each time they touch NIC
> configuration.

To clarify, the configuration operation itself completes before
returning to userspace. However, the short link-down during the
configuration triggers asynchronous systemd events. These userspace
operations affect the subsequent pings. Sorry for not making this
clear in the commit message.

Regarding the 10s delay: I agree it is long. In my environment, the
interface stabilizes in under 1s. I chose 10s only to maintain
consistency with existing delays in this test script. I'm happy to
reduce this to a smaller value (say, 3s) in v2.

Regards,
Pin-yen

>
> --
> pw-bot: reject