APPLIED[U]: Re: [SRU][R/Q/P/N/J][PATCH 0/1] i40e: avoid redundant VF link state updates

[Paolo Pisati]

On Mon, Nov 03, 2025 at 04:40:29PM +0100, Robert Malz wrote:
> BugLink: https://bugs.launchpad.net/bugs/2130552
> 
> [ Impact ]
> 
>  * In the i40e driver, every VF link state change request is causing a VF reset,
>    even if the requested change is already set. This leads to unnecessary VF
>    resets and can cause performance degradation or instability in the VF
>    driver, particularly in DPDK environments.
> 
>  * With the proposed patch, i40e will skip VF link state change requests when the
>    desired link state matches the current configuration. This prevents
>    unnecessary VF resets and reduces PF-VF communication overhead.
> 
>  * The issue was originally detected by analyzing DPDK VF driver issues during
>    OpenStack Neutron restarts. In such cases, i40e will issue an unnecessary VF
>    reset request which causes instability in the DPDK driver.
> 
> [ Test Plan ]
> 
>  * The issue can be reproduced by triggering VF link state changes multiple times
>    with the same requested link state.
> 
>  * To reproduce the problem, run the following command multiple times
>    on the same interface: 'ip link set <ifname> vf 0 state auto'.
>    Every time the command is executed, the PF driver will trigger a VF reset.
> 
>  * Monitor for VF reset events using dmesg or appropriate logging mechanisms
>    to confirm the issue and verify the fix.
> 
>  * Regression testing should include:
>    - Verify normal VF link state changes still work correctly when state actually changes
>    - Validate that legitimate state changes still trigger resets when needed
> 
> [ Where problems could occur ]
> 
>  * Changes only affect the i40e .ndo_set_vf_link_state routine. In case
>    of any regressions, only the ability to set VF link state changes could be
>    impacted.
> 
>  * The patch was verified locally and passed Intel internal test execution.
> 
>  * Potential failure modes:
>    - Logic error in state comparison could prevent legitimate state changes
>    - Incorrect state tracking could lead to inconsistent VF behavior
> 
>  * Risk mitigation:
>    - The change is isolated to a specific code path in the i40e driver
>    - Existing VF functionality remains unchanged when state changes are needed
>    - The patch adds a simple comparison check before existing link change routine
> 
> [ Other Info ]
> 
>  * At the time of writing this document, the target patch is still in the net-next
>    tree and has not yet been merged into linux-next.
> 
>  * Patch: a7ae783da0b919550e260aebfca1c6ef030b99a4 from netdev/net-next
> 
>  * Patch applies on most versions without any conflicts
> 
>  * No dependencies on other patches
> 
>  * Backport requirements: Patch should apply cleanly to Ubuntu kernel versions
> 
>  * VF reset during link state change was added as a part of 31deb12e85c35ddd2c037f0107d05d8674cab2c0 (upstream) commit, which is included in the Kernels starting from 5.15
> 
> Jay Vosburgh (1):
>   i40e: avoid redundant VF link state updates
> 
>  drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> -- 
> 2.34.1
> 
> 
> -- 
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

-- 
bye,
p.