[PATCH 1/1] i40e: avoid redundant VF link state updates

[Robert Malz]

From: Jay Vosburgh <jay.vosburgh at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/2130552

Multiple sources can request VF link state changes with identical
parameters. For example, OpenStack Neutron may request to set the VF link
state to IFLA_VF_LINK_STATE_AUTO during every initialization or user can
issue: `ip link set <ifname> vf 0 state auto` multiple times. Currently,
the i40e driver processes each of these requests, even if the requested
state is the same as the current one. This leads to unnecessary VF resets
and can cause performance degradation or instability in the VF driver,
particularly in environment using Data Plane Development Kit (DPDK).

With this 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.

To reproduce the problem run following command multiple times
on the same interface: 'ip link set <ifname> vf 0 state auto'
Every time command is executed, PF driver will trigger VF reset.

Co-developed-by: Robert Malz <robert.malz at canonical.com>
Signed-off-by: Robert Malz <robert.malz at canonical.com>
Signed-off-by: Jay Vosburgh <jay.vosburgh at canonical.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov at intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski at intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen at intel.com>
(cherry picked from commit a7ae783da0b919550e260aebfca1c6ef030b99a4 net-next)
Signed-off-by: Robert Malz <robert.malz at canonical.com>

---
 drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
index 081a4526a2f0..0fe0d52c796b 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
@@ -4788,6 +4788,7 @@ int i40e_ndo_set_vf_link_state(struct net_device *netdev, int vf_id, int link)
 	unsigned long q_map;
 	struct i40e_vf *vf;
 	int abs_vf_id;
+	int old_link;
 	int ret = 0;
 	int tmp;
 
@@ -4806,6 +4807,17 @@ int i40e_ndo_set_vf_link_state(struct net_device *netdev, int vf_id, int link)
 	vf = &pf->vf[vf_id];
 	abs_vf_id = vf->vf_id + hw->func_caps.vf_base_id;
 
+	/* skip VF link state change if requested state is already set */
+	if (!vf->link_forced)
+		old_link = IFLA_VF_LINK_STATE_AUTO;
+	else if (vf->link_up)
+		old_link = IFLA_VF_LINK_STATE_ENABLE;
+	else
+		old_link = IFLA_VF_LINK_STATE_DISABLE;
+
+	if (link == old_link)
+		goto error_out;
+
 	pfe.event = VIRTCHNL_EVENT_LINK_CHANGE;
 	pfe.severity = PF_EVENT_SEVERITY_INFO;
 
-- 
2.34.1