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

[Mehmet Basaran]

Acked-by: Mehmet Basaran <mehmet.basaran at canonical.com>

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Robert Malz <robert.malz at canonical.com> writes:

> 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
>
>
> -- 
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> kernel-team at lists.ubuntu.com
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