i40e: Simplify i40e_detect_recover_hung_queue logic

This patch greatly reduces the unneeded complexity in the
i40e_detect_recover_hung_queue code path.  The previous implementation
set a 'hung bit' which would then get cleared while polling.  If the
detection routine was called a second time with the bit already set, we
would issue a software interrupt.  This patch makes it such that if
interrupts are disabled and we have pending TX descriptors, we trigger a
software interrupt since in, the worst case, queues are already clean
and we have an extra interrupt.

Additionally this patch removes the workaround for lost interrupts as
calling napi_reschedule in this context can cause software interrupts to
fire on the wrong CPU.

Change-ID: Iae108582a3ceb6229ed1d22e4ed6e69cf97aad8d
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 11 insertions, 48 deletions

diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index 8181647f512e..22831a4a9099 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -737,7 +737,6 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
         struct i40e_eth_stats *oes;
         struct i40e_eth_stats *es;     /* device's eth stats */
         u32 tx_restart, tx_busy;
-        u64 tx_lost_interrupt;
         struct i40e_ring *p;
         u32 rx_page, rx_buf;
         u64 bytes, packets;
@@ -763,7 +762,6 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
         rx_b = rx_p = 0;
         tx_b = tx_p = 0;
         tx_restart = tx_busy = tx_linearize = tx_force_wb = 0;
-        tx_lost_interrupt = 0;
         rx_page = 0;
         rx_buf = 0;
         rcu_read_lock();
@@ -782,7 +780,6 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
                 tx_busy += p->tx_stats.tx_busy;
                 tx_linearize += p->tx_stats.tx_linearize;
                 tx_force_wb += p->tx_stats.tx_force_wb;
-                tx_lost_interrupt += p->tx_stats.tx_lost_interrupt;
 
                 /* Rx queue is part of the same block as Tx queue */
                 p = &p[1];
@@ -801,7 +798,6 @@ static void i40e_update_vsi_stats(struct i40e_vsi *vsi)
         vsi->tx_busy = tx_busy;
         vsi->tx_linearize = tx_linearize;
         vsi->tx_force_wb = tx_force_wb;
-        vsi->tx_lost_interrupt = tx_lost_interrupt;
         vsi->rx_page_failed = rx_page;
         vsi->rx_buf_failed = rx_buf;
 
@@ -4508,16 +4504,15 @@ static int i40e_pf_wait_queues_disabled(struct i40e_pf *pf)
  * @vsi: Pointer to VSI struct
  *
  * This function checks specified queue for given VSI. Detects hung condition.
- * Sets hung bit since it is two step process. Before next run of service task
- * if napi_poll runs, it reset 'hung' bit for respective q_vector. If not,
- * hung condition remain unchanged and during subsequent run, this function
- * issues SW interrupt to recover from hung condition.
+ * We proactively detect hung TX queues by checking if interrupts are disabled
+ * but there are pending descriptors.  If it appears hung, attempt to recover
+ * by triggering a SW interrupt.
  **/
 static void i40e_detect_recover_hung_queue(int q_idx, struct i40e_vsi *vsi)
 {
         struct i40e_ring *tx_ring = NULL;
         struct i40e_pf  *pf;
-        u32 head, val, tx_pending_hw;
+        u32 val, tx_pending;
         int i;
 
         pf = vsi->back;
@@ -4543,47 +4538,15 @@ static void i40e_detect_recover_hung_queue(int q_idx, struct i40e_vsi *vsi)
         else
                 val = rd32(&pf->hw, I40E_PFINT_DYN_CTL0);
 
-        head = i40e_get_head(tx_ring);
+        tx_pending = i40e_get_tx_pending(tx_ring);
 
-        tx_pending_hw = i40e_get_tx_pending(tx_ring, false);
-
-        /* HW is done executing descriptors, updated HEAD write back,
-         * but SW hasn't processed those descriptors. If interrupt is
-         * not generated from this point ON, it could result into
-         * dev_watchdog detecting timeout on those netdev_queue,
-         * hence proactively trigger SW interrupt.
+        /* Interrupts are disabled and TX pending is non-zero,
+         * trigger the SW interrupt (don't wait). Worst case
+         * there will be one extra interrupt which may result
+         * into not cleaning any queues because queues are cleaned.
          */
-        if (tx_pending_hw && (!(val & I40E_PFINT_DYN_CTLN_INTENA_MASK))) {
-                /* NAPI Poll didn't run and clear since it was set */
-                if (test_and_clear_bit(I40E_Q_VECTOR_HUNG_DETECT,
-                                       &tx_ring->q_vector->hung_detected)) {
-                        netdev_info(vsi->netdev, "VSI_seid %d, Hung TX queue %d, tx_pending_hw: %d, NTC:0x%x, HWB: 0x%x, NTU: 0x%x, TAIL: 0x%x\n",
-                                    vsi->seid, q_idx, tx_pending_hw,
-                                    tx_ring->next_to_clean, head,
-                                    tx_ring->next_to_use,
-                                    readl(tx_ring->tail));
-                        netdev_info(vsi->netdev, "VSI_seid %d, Issuing force_wb for TX queue %d, Interrupt Reg: 0x%x\n",
-                                    vsi->seid, q_idx, val);
-                        i40e_force_wb(vsi, tx_ring->q_vector);
-                } else {
-                        /* First Chance - detected possible hung */
-                        set_bit(I40E_Q_VECTOR_HUNG_DETECT,
-                                &tx_ring->q_vector->hung_detected);
-                }
-        }
-
-        /* This is the case where we have interrupts missing,
-         * so the tx_pending in HW will most likely be 0, but we
-         * will have tx_pending in SW since the WB happened but the
-         * interrupt got lost.
-         */
-        if ((!tx_pending_hw) && i40e_get_tx_pending(tx_ring, true) &&
-            (!(val & I40E_PFINT_DYN_CTLN_INTENA_MASK))) {
-                local_bh_disable();
-                if (napi_reschedule(&tx_ring->q_vector->napi))
-                        tx_ring->tx_stats.tx_lost_interrupt++;
-                local_bh_enable();
-        }
+        if (tx_pending && (!(val & I40E_PFINT_DYN_CTLN_INTENA_MASK)))
+                i40e_force_wb(vsi, tx_ring->q_vector);
 }
 
 /**