Re: [PATCH iwl-next v5 2/2] igc: Link queues to NAPI instances

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On 10/28/2024 9:52 PM, Joe Damato wrote:
Link queues to NAPI instances via netdev-genl API so that users can
query this information with netlink. Handle a few cases in the driver:
   1. Link/unlink the NAPIs when XDP is enabled/disabled
   2. Handle IGC_FLAG_QUEUE_PAIRS enabled and disabled

Example output when IGC_FLAG_QUEUE_PAIRS is enabled:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                          --dump queue-get --json='{"ifindex": 2}'

[{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
  {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
  {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'rx'},
  {'id': 3, 'ifindex': 2, 'napi-id': 8196, 'type': 'rx'},
  {'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'tx'},
  {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'tx'},
  {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'tx'},
  {'id': 3, 'ifindex': 2, 'napi-id': 8196, 'type': 'tx'}]

Since IGC_FLAG_QUEUE_PAIRS is enabled, you'll note that the same NAPI ID
is present for both rx and tx queues at the same index, for example
index 0:

{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'tx'},

To test IGC_FLAG_QUEUE_PAIRS disabled, a test system was booted using
the grub command line option "maxcpus=2" to force
igc_set_interrupt_capability to disable IGC_FLAG_QUEUE_PAIRS.

Example output when IGC_FLAG_QUEUE_PAIRS is disabled:

$ lscpu | grep "On-line CPU"
On-line CPU(s) list:      0,2

$ ethtool -l enp86s0  | tail -5
Current hardware settings:
RX:		n/a
TX:		n/a
Other:		1
Combined:	2

$ cat /proc/interrupts  | grep enp
  144: [...] enp86s0
  145: [...] enp86s0-rx-0
  146: [...] enp86s0-rx-1
  147: [...] enp86s0-tx-0
  148: [...] enp86s0-tx-1

1 "other" IRQ, and 2 IRQs for each of RX and Tx, so we expect netlink to
report 4 IRQs with unique NAPI IDs:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                          --dump napi-get --json='{"ifindex": 2}'
[{'id': 8196, 'ifindex': 2, 'irq': 148},
  {'id': 8195, 'ifindex': 2, 'irq': 147},
  {'id': 8194, 'ifindex': 2, 'irq': 146},
  {'id': 8193, 'ifindex': 2, 'irq': 145}]

Now we examine which queues these NAPIs are associated with, expecting
that since IGC_FLAG_QUEUE_PAIRS is disabled each RX and TX queue will
have its own NAPI instance:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                          --dump queue-get --json='{"ifindex": 2}'
[{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
  {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
  {'id': 0, 'ifindex': 2, 'napi-id': 8195, 'type': 'tx'},
  {'id': 1, 'ifindex': 2, 'napi-id': 8196, 'type': 'tx'}]

Signed-off-by: Joe Damato <jdamato@xxxxxxxxxx>
---
  v5:
    - Rename igc_resume to __igc_do_resume and pass in a boolean
      "need_rtnl" to signal whether or not rtnl should be held before
      caling __igc_open. Call this new function from igc_runtime_resume
      and igc_resume passing in false (for igc_runtime_resume) and true
      (igc_resume), respectively. This is done to avoid reintroducing a
      bug fixed in commit: 6f31d6b: "igc: Refactor runtime power
      management flow" where rtnl is held in runtime_resume causing a
      deadlock.

  v4:
    - Add rtnl_lock/rtnl_unlock in two paths: igc_resume and
      igc_io_error_detected. The code added to the latter is inspired by
      a similar implementation in ixgbe's ixgbe_io_error_detected.

  v3:
    - Replace igc_unset_queue_napi with igc_set_queue_napi(adapater, i,
      NULL), as suggested by Vinicius Costa Gomes
    - Simplify implemention of igc_set_queue_napi as suggested by Kurt
      Kanzenbach, with a tweak to use ring->queue_index

  v2:
    - Update commit message to include tests for IGC_FLAG_QUEUE_PAIRS
      disabled
    - Refactored code to move napi queue mapping and unmapping to helper
      functions igc_set_queue_napi and igc_unset_queue_napi
    - Adjust the code to handle IGC_FLAG_QUEUE_PAIRS disabled
    - Call helpers to map/unmap queues to NAPIs in igc_up, __igc_open,
      igc_xdp_enable_pool, and igc_xdp_disable_pool

  drivers/net/ethernet/intel/igc/igc.h      |  2 +
  drivers/net/ethernet/intel/igc/igc_main.c | 52 ++++++++++++++++++++---
  drivers/net/ethernet/intel/igc/igc_xdp.c  |  2 +
  3 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index eac0f966e0e4..b8111ad9a9a8 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -337,6 +337,8 @@ struct igc_adapter {
  	struct igc_led_classdev *leds;
  };
+void igc_set_queue_napi(struct igc_adapter *adapter, int q_idx,
+			struct napi_struct *napi);
  void igc_up(struct igc_adapter *adapter);
  void igc_down(struct igc_adapter *adapter);
  int igc_open(struct net_device *netdev);
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 7964bbedb16c..051a0cdb1143 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -4948,6 +4948,22 @@ static int igc_sw_init(struct igc_adapter *adapter)
  	return 0;
  }
+void igc_set_queue_napi(struct igc_adapter *adapter, int vector,
+			struct napi_struct *napi)
+{
+	struct igc_q_vector *q_vector = adapter->q_vector[vector];
+
+	if (q_vector->rx.ring)
+		netif_queue_set_napi(adapter->netdev,
+				     q_vector->rx.ring->queue_index,
+				     NETDEV_QUEUE_TYPE_RX, napi);
+
+	if (q_vector->tx.ring)
+		netif_queue_set_napi(adapter->netdev,
+				     q_vector->tx.ring->queue_index,
+				     NETDEV_QUEUE_TYPE_TX, napi);
+}
+
  /**
   * igc_up - Open the interface and prepare it to handle traffic
   * @adapter: board private structure
@@ -4955,6 +4971,7 @@ static int igc_sw_init(struct igc_adapter *adapter)
  void igc_up(struct igc_adapter *adapter)
  {
  	struct igc_hw *hw = &adapter->hw;
+	struct napi_struct *napi;
  	int i = 0;
/* hardware has been reset, we need to reload some things */
@@ -4962,8 +4979,11 @@ void igc_up(struct igc_adapter *adapter)
clear_bit(__IGC_DOWN, &adapter->state); - for (i = 0; i < adapter->num_q_vectors; i++)
-		napi_enable(&adapter->q_vector[i]->napi);
+	for (i = 0; i < adapter->num_q_vectors; i++) {
+		napi = &adapter->q_vector[i]->napi;
+		napi_enable(napi);
+		igc_set_queue_napi(adapter, i, napi);
+	}
if (adapter->msix_entries)
  		igc_configure_msix(adapter);
@@ -5192,6 +5212,7 @@ void igc_down(struct igc_adapter *adapter)
  	for (i = 0; i < adapter->num_q_vectors; i++) {
  		if (adapter->q_vector[i]) {
  			napi_synchronize(&adapter->q_vector[i]->napi);
+			igc_set_queue_napi(adapter, i, NULL);
  			napi_disable(&adapter->q_vector[i]->napi);
  		}
  	}
@@ -6021,6 +6042,7 @@ static int __igc_open(struct net_device *netdev, bool resuming)
  	struct igc_adapter *adapter = netdev_priv(netdev);
  	struct pci_dev *pdev = adapter->pdev;
  	struct igc_hw *hw = &adapter->hw;
+	struct napi_struct *napi;
  	int err = 0;
  	int i = 0;
@@ -6056,8 +6078,11 @@ static int __igc_open(struct net_device *netdev, bool resuming) clear_bit(__IGC_DOWN, &adapter->state); - for (i = 0; i < adapter->num_q_vectors; i++)
-		napi_enable(&adapter->q_vector[i]->napi);
+	for (i = 0; i < adapter->num_q_vectors; i++) {
+		napi = &adapter->q_vector[i]->napi;
+		napi_enable(napi);
+		igc_set_queue_napi(adapter, i, napi);
+	}
/* Clear any pending interrupts. */
  	rd32(IGC_ICR);
@@ -7342,7 +7367,7 @@ static void igc_deliver_wake_packet(struct net_device *netdev)
  	netif_rx(skb);
  }
-static int igc_resume(struct device *dev)
+static int __igc_do_resume(struct device *dev, bool need_rtnl)
  {
  	struct pci_dev *pdev = to_pci_dev(dev);
  	struct net_device *netdev = pci_get_drvdata(pdev);
@@ -7385,7 +7410,11 @@ static int igc_resume(struct device *dev)
  	wr32(IGC_WUS, ~0);
if (netif_running(netdev)) {
+		if (need_rtnl)
+			rtnl_lock();
  		err = __igc_open(netdev, true);
+		if (need_rtnl)
+			rtnl_unlock();
  		if (!err)
  			netif_device_attach(netdev);
  	}
@@ -7393,9 +7422,14 @@ static int igc_resume(struct device *dev)
  	return err;
  }
+static int igc_resume(struct device *dev)
+{
+	return __igc_do_resume(dev, true);
+}
+
  static int igc_runtime_resume(struct device *dev)
  {
-	return igc_resume(dev);
+	return __igc_do_resume(dev, false);
  }
static int igc_suspend(struct device *dev)
@@ -7440,14 +7474,18 @@ static pci_ers_result_t igc_io_error_detected(struct pci_dev *pdev,
  	struct net_device *netdev = pci_get_drvdata(pdev);
  	struct igc_adapter *adapter = netdev_priv(netdev);
+ rtnl_lock();
  	netif_device_detach(netdev);
- if (state == pci_channel_io_perm_failure)
+	if (state == pci_channel_io_perm_failure) {
+		rtnl_unlock();
  		return PCI_ERS_RESULT_DISCONNECT;
+	}
if (netif_running(netdev))
  		igc_down(adapter);
  	pci_disable_device(pdev);
+	rtnl_unlock();
/* Request a slot reset. */
  	return PCI_ERS_RESULT_NEED_RESET;
diff --git a/drivers/net/ethernet/intel/igc/igc_xdp.c b/drivers/net/ethernet/intel/igc/igc_xdp.c
index e27af72aada8..4da633430b80 100644
--- a/drivers/net/ethernet/intel/igc/igc_xdp.c
+++ b/drivers/net/ethernet/intel/igc/igc_xdp.c
@@ -84,6 +84,7 @@ static int igc_xdp_enable_pool(struct igc_adapter *adapter,
  		napi_disable(napi);
  	}
+ igc_set_queue_napi(adapter, queue_id, NULL);
  	set_bit(IGC_RING_FLAG_AF_XDP_ZC, &rx_ring->flags);
  	set_bit(IGC_RING_FLAG_AF_XDP_ZC, &tx_ring->flags);
@@ -133,6 +134,7 @@ static int igc_xdp_disable_pool(struct igc_adapter *adapter, u16 queue_id)
  	xsk_pool_dma_unmap(pool, IGC_RX_DMA_ATTR);
  	clear_bit(IGC_RING_FLAG_AF_XDP_ZC, &rx_ring->flags);
  	clear_bit(IGC_RING_FLAG_AF_XDP_ZC, &tx_ring->flags);
+	igc_set_queue_napi(adapter, queue_id, napi);
if (needs_reset) {
  		napi_enable(napi);

I believe that this fix should work on most cases. I have some concerns that this solution might not be 100% robust as sometimes runtime resume may be triggered without the rtnl being held. For example, if it is initiated by a network wake event. But, for the moment I think that this appoach is good enough.

My main comment here is the naming conventions, I prefer using the original parameters/function names for consistency, similarly to what was done in the igb driver:
https://github.com/torvalds/linux/commit/ac8c58f5b535d6272324e2b8b4a0454781c9147e





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