i40e/i40evf: Add support for new mechanism of updating adaptive ITR

This patch replaces the existing mechanism for determining the correct
value to program for adaptive ITR with yet another new and more
complicated approach.

The basic idea from a 30K foot view is that this new approach will push the
Rx interrupt moderation up so that by default it starts in low latency and
is gradually pushed up into a higher latency setup as long as doing so
increases the number of packets processed, if the number of packets drops
to 4 to 1 per packet we will reset and just base our ITR on the size of the
packets being received. For Tx we leave it floating at a high interrupt
delay and do not pull it down unless we start processing more than 112
packets per interrupt. If we start exceeding that we will cut our interrupt
rates in half until we are back below 112.

The side effect of these patches are that we will be processing more
packets per interrupt. This is both a good and a bad thing as it means we
will not be blocking processing in the case of things like pktgen and XDP,
but we will also be consuming a bit more CPU in the cases of things such as
network throughput tests using netperf.

One delta from this versus the ixgbe version of the changes is that I have
made the interrupt moderation a bit more aggressive when we are in bulk
mode by moving our "goldilocks zone" up from 48 to 96 to 56 to 112. The
main motivation behind moving this is to address the fact that we need to
update less frequently, and have more fine grained control due to the
separate Tx and Rx ITR times.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e.h

@@ -824,6 +824,7 @@ struct i40e_q_vector {
 	struct i40e_ring_container rx;
 	struct i40e_ring_container tx;
 
+	u8 itr_countdown;	/* when 0 should adjust adaptive ITR */
 	u8 num_ringpairs;	/* total number of ring pairs in vector */
 
 	cpumask_t affinity_mask;
@@ -832,8 +833,6 @@ struct i40e_q_vector {
 	struct rcu_head rcu;	/* to avoid race with update stats on free */
 	char name[I40E_INT_NAME_STR_LEN];
 	bool arm_wb_state;
-#define ITR_COUNTDOWN_START 100
-	u8 itr_countdown;	/* when 0 should adjust ITR */
 } ____cacheline_internodealigned_in_smp;
 
 /* lan device */

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -3449,19 +3449,20 @@ static void i40e_vsi_configure_msix(struct i40e_vsi *vsi)
 	for (i = 0; i < vsi->num_q_vectors; i++, vector++) {
 		struct i40e_q_vector *q_vector = vsi->q_vectors[i];
 
-		q_vector->itr_countdown = ITR_COUNTDOWN_START;
+		q_vector->rx.next_update = jiffies + 1;
 		q_vector->rx.target_itr =
 			ITR_TO_REG(vsi->rx_rings[i]->itr_setting);
-		q_vector->rx.latency_range = I40E_LOW_LATENCY;
 		wr32(hw, I40E_PFINT_ITRN(I40E_RX_ITR, vector - 1),
 		     q_vector->rx.target_itr);
 		q_vector->rx.current_itr = q_vector->rx.target_itr;
+
+		q_vector->tx.next_update = jiffies + 1;
 		q_vector->tx.target_itr =
 			ITR_TO_REG(vsi->tx_rings[i]->itr_setting);
-		q_vector->tx.latency_range = I40E_LOW_LATENCY;
 		wr32(hw, I40E_PFINT_ITRN(I40E_TX_ITR, vector - 1),
 		     q_vector->tx.target_itr);
 		q_vector->tx.current_itr = q_vector->tx.target_itr;
+
 		wr32(hw, I40E_PFINT_RATEN(vector - 1),
 		     i40e_intrl_usec_to_reg(vsi->int_rate_limit));
 
@@ -3562,13 +3563,12 @@ static void i40e_configure_msi_and_legacy(struct i40e_vsi *vsi)
 	u32 val;
 
 	/* set the ITR configuration */
-	q_vector->itr_countdown = ITR_COUNTDOWN_START;
+	q_vector->rx.next_update = jiffies + 1;
 	q_vector->rx.target_itr = ITR_TO_REG(vsi->rx_rings[0]->itr_setting);
-	q_vector->rx.latency_range = I40E_LOW_LATENCY;
 	wr32(hw, I40E_PFINT_ITR0(I40E_RX_ITR), q_vector->rx.target_itr);
 	q_vector->rx.current_itr = q_vector->rx.target_itr;
+	q_vector->tx.next_update = jiffies + 1;
 	q_vector->tx.target_itr = ITR_TO_REG(vsi->tx_rings[0]->itr_setting);
-	q_vector->tx.latency_range = I40E_LOW_LATENCY;
 	wr32(hw, I40E_PFINT_ITR0(I40E_TX_ITR), q_vector->tx.target_itr);
 	q_vector->tx.current_itr = q_vector->tx.target_itr;
 
@@ -10345,9 +10345,6 @@ static int i40e_vsi_alloc_q_vector(struct i40e_vsi *vsi, int v_idx, int cpu)
 		netif_napi_add(vsi->netdev, &q_vector->napi,
 			       i40e_napi_poll, NAPI_POLL_WEIGHT);
 
-	q_vector->rx.latency_range = I40E_LOW_LATENCY;
-	q_vector->tx.latency_range = I40E_LOW_LATENCY;
-
 	/* tie q_vector and vsi together */
 	vsi->q_vectors[v_idx] = q_vector;