Re: [PATCH net-next 1/1] ice: Improve MSI-X vector enablement fallback logic

On Wed, 13 Jan 2021 15:42:26 -0800 Tony Nguyen wrote:

From: Brett Creeley <redacted>

The current MSI-X enablement logic either tries to enable best-case
MSI-X vectors and if that fails we only support a bare-minimum set.
This is not very flexible and the current logic is broken when actually
allocating and reserving MSI-X in the driver. Fix this by improving the
fall-back logic and fixing the allocation/reservation of MSI-X when the
best-case MSI-X vectors are not received from the OS.

The new fall-back logic is described below with each [#] being an
attempt at enabling a certain number of MSI-X. If any of the steps
succeed, then return the number of MSI-X enabled from
ice_ena_msix_range(). If any of the attempts fail, then goto the next
step.

Attempt [0]: Enable the best-case scenario MSI-X vectors.

Attempt [1]: Enable MSI-X vectors with the number of pf->num_lan_msix
reduced by a factor of 2 from the previous attempt (i.e.
num_online_cpus() / 2).

Attempt [2]: Same as attempt [1], except reduce by a factor of 4.

Attempt [3]: Enable the bare-minimum MSI-X vectors.

Also, if the adjusted_base_msix ever hits the minimum required for LAN,
then just set the needed MSI-X for that feature to the minimum
(similar to attempt [3]).

I don't really get why you switch to this manual "exponential back-off"
rather than continuing to use pci_enable_msix_range(), but fixing the
capping to ICE_MIN_LAN_VECS.

To fix the allocation/reservation of MSI-X, the PF VSI needs to take
into account the pf->num_lan_msix available and only allocate up to that
many MSI-X vectors. To do this, limit the number of Tx and Rx queues
based on pf->num_lan_msix. This is done because we don't want more than
1 Tx/Rx queue per interrupt due to performance concerns. Also, limit the
number of MSI-X based on pf->num_lan_msix available.

Also, prevent users from enabling more combined queues than there are
MSI-X available via ethtool.

Right, this part sounds like a fix, and should be a separate patch
against net, not net-next.

Fixes: 152b978a1f90 ("ice: Rework ice_ena_msix_range")
Signed-off-by: Brett Creeley <redacted>
Tested-by: Tony Brelinski <redacted>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>