Subject: Re: [PATCH iwl-net] i40e: keep q_vectors array in sync with channel count changes

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 16 Apr 2026 13:12:53 +0200

On Tue, Apr 14, 2026 at 02:14:05PM +0200, Maciej Fijalkowski wrote:
> For the main VSI, i40e_set_num_rings_in_vsi() always derives
> num_q_vectors from pf->num_lan_msix. At the same time, ethtool -L stores
> the user requested channel count in vsi->req_queue_pairs and the queue
> setup path uses that value for the effective number of queue pairs.
> 
> This leaves queue and vector counts out of sync after shrinking channel
> count via ethtool -L. The active queue configuration is reduced, but the
> VSI still keeps the full PF-sized q_vector topology.
> 
> That mismatch breaks reconfiguration flows which rely on vector/NAPI
> state matching the effective channel configuration. In particular,
> toggling /sys/class/net/<dev>/threaded after reducing the channel count
> can hang, and later channel-count changes can fail because VSI reinit
> does not rebuild q_vectors to match the new vector count.
> 
> Fix this by making the main VSI num_q_vectors follow the effective
> requested channel count, capped by the available MSI-X vectors. Update
> i40e_vsi_reinit_setup() to rebuild q_vectors during VSI reinit so the
> vector topology is refreshed together with the ring arrays when channel
> count changes.
> 
> Keep alloc_queue_pairs unchanged and based on pf->num_lan_qps so the VSI
> retains its full queue capacity.
> 
> Selftest napi_threaded.py was originally used when Jakub reported hang
> on /sys/class/net/<dev>/threaded toggle. In order to make it pass on
> i40e, use persistent NAPI configuration for q_vector NAPIs so NAPI
> identity and threaded settings survive q_vector reallocation across
> channel-count changes. This is achieved by using netif_napi_add_config()
> when configuring q_vectors.
> 
> $ export NETIF=ens259f1np1
> $ sudo -E env PATH="$PATH" ./tools/testing/selftests/drivers/net/napi_threaded.py
> TAP version 13
> 1..3
> ok 1 napi_threaded.napi_init
> ok 2 napi_threaded.change_num_queues
> ok 3 napi_threaded.enable_dev_threaded_disable_napi_threaded
> Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Reported-by: Jakub Kicinski <[email-masked]>
> Closes: https://lore.kernel.org/intel-wired-lan/[email-masked]/
> Fixes: d2a69fefd756 ("i40e: Fix changing previously set num_queue_pairs for PFs")
> Signed-off-by: Maciej Fijalkowski <[email-masked]>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 34 +++++++++++++++++----
>  1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 926d001b2150..5636ad71f940 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -11403,10 +11403,14 @@ static void i40e_service_timer(struct timer_list *t)
>  static int i40e_set_num_rings_in_vsi(struct i40e_vsi *vsi)
>  {
>  	struct i40e_pf *pf = vsi->back;
> +	u16 qps;
>  
>  	switch (vsi->type) {
>  	case I40E_VSI_MAIN:
>  		vsi->alloc_queue_pairs = pf->num_lan_qps;
> +		qps = vsi->req_queue_pairs ?
> +		      min_t(u16, vsi->req_queue_pairs, pf->num_lan_qps) :
> +		      pf->num_lan_qps;
>  		if (!vsi->num_tx_desc)
>  			vsi->num_tx_desc = ALIGN(I40E_DEFAULT_NUM_DESCRIPTORS,
>  						 I40E_REQ_DESCRIPTOR_MULTIPLE);
> @@ -11414,7 +11418,8 @@ static int i40e_set_num_rings_in_vsi(struct i40e_vsi *vsi)
>  			vsi->num_rx_desc = ALIGN(I40E_DEFAULT_NUM_DESCRIPTORS,
>  						 I40E_REQ_DESCRIPTOR_MULTIPLE);
>  		if (test_bit(I40E_FLAG_MSIX_ENA, pf->flags))
> -			vsi->num_q_vectors = pf->num_lan_msix;
> +			vsi->num_q_vectors = max_t(int, 1,
> +						   min_t(int, qps, pf->num_lan_msix));
>  		else
>  			vsi->num_q_vectors = 1;
>  
> @@ -12043,7 +12048,8 @@ static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx)
>  	cpumask_copy(&q_vector->affinity_mask, cpu_possible_mask);
>  
>  	if (vsi->netdev)
> -		netif_napi_add(vsi->netdev, &q_vector->napi, i40e_napi_poll);
> +		netif_napi_add_config(vsi->netdev, &q_vector->napi,
> +				      i40e_napi_poll, v_idx);
>  
>  	/* tie q_vector and vsi together */
>  	vsi->q_vectors[v_idx] = q_vector;
> @@ -14265,12 +14271,27 @@ static struct i40e_vsi *i40e_vsi_reinit_setup(struct i40e_vsi *vsi)
>  
>  	pf = vsi->back;
>  
> +	if (test_bit(I40E_FLAG_MSIX_ENA, pf->flags)) {
> +		i40e_put_lump(pf->irq_pile, vsi->base_vector, vsi->idx);
> +		vsi->base_vector = 0;
> +	}
> +
>  	i40e_put_lump(pf->qp_pile, vsi->base_queue, vsi->idx);
>  	i40e_vsi_clear_rings(vsi);
>  
> -	i40e_vsi_free_arrays(vsi, false);
> +	i40e_vsi_free_q_vectors(vsi);
> +	i40e_vsi_free_arrays(vsi, true);
>  	i40e_set_num_rings_in_vsi(vsi);
> -	ret = i40e_vsi_alloc_arrays(vsi, false);
> +
> +	ret = i40e_vsi_alloc_arrays(vsi, true);
> +	if (ret)
> +		goto err_vsi;

Sashiko warns about potential double-free on vsi->tx_rings. I will send a
v2 where I include NULLing this ptr in i40e_vsi_alloc_arrays().

Thanks,
Maciej

> +
> +	/* Rebuild q_vectors during VSI reinit because the effective channel
> +	 * count may change num_q_vectors. Keep vector topology aligned with the
> +	 * queue configuration after ethtool's .set_channels() callback.
> +	 */
> +	ret = i40e_vsi_setup_vectors(vsi);
>  	if (ret)
>  		goto err_vsi;
>  
> @@ -14282,7 +14303,7 @@ static struct i40e_vsi *i40e_vsi_reinit_setup(struct i40e_vsi *vsi)
>  		dev_info(&pf->pdev->dev,
>  			 "failed to get tracking for %d queues for VSI %d err %d\n",
>  			 alloc_queue_pairs, vsi->seid, ret);
> -		goto err_vsi;
> +		goto err_lump;
>  	}
>  	vsi->base_queue = ret;
>  
> @@ -14306,7 +14327,6 @@ static struct i40e_vsi *i40e_vsi_reinit_setup(struct i40e_vsi *vsi)
>  	return vsi;
>  
>  err_rings:
> -	i40e_vsi_free_q_vectors(vsi);
>  	if (vsi->netdev_registered) {
>  		vsi->netdev_registered = false;
>  		unregister_netdev(vsi->netdev);
> @@ -14316,6 +14336,8 @@ static struct i40e_vsi *i40e_vsi_reinit_setup(struct i40e_vsi *vsi)
>  	if (vsi->type == I40E_VSI_MAIN)
>  		i40e_devlink_destroy_port(pf);
>  	i40e_aq_delete_element(&pf->hw, vsi->seid, NULL);
> +err_lump:
> +	i40e_vsi_free_q_vectors(vsi);
>  err_vsi:
>  	i40e_vsi_clear(vsi);
>  	return NULL;
> -- 
> 2.43.0
>