i40e/i40evf: moderate interrupts differently

The XL710 hardware has a different interrupt moderation design
that can support a limit of total interrupts per second per
vector, in addition to the "number of interrupts per second"
controls already established in the driver.  This combination
of hardware features allows us to set very low default latency
settings but minimize the total CPU utilization by not
making too many interrupts, should the user desire.

The current driver implementation is still enabling the dynamic
moderation in the driver, and only using the rx/tx-usecs
limit in ethtool to limit the interrupt rate per second, by default.

The new code implemented in this patch
2) adds init/use of the new "Interrupt Limit" register
3) adds ethtool knob to control/report the limits above

Usage is ethtool -C ethx rx-usecs-high <value> Where <value> is number
of microseconds to create a rate of 1/N interrupts per second,
regardless of rx-usecs or tx-usecs values. Since there is a credit based
scheme in the hardware, the rx-usecs and tx-usecs can be configured for
very low latency for short bursts, but once the credit runs out the
refill rate on the credits is limited by rx-usecs-high.

Change-ID: I3a1075d3296123b0f4f50623c779b027af5b188d
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
index cb88e7abfe8d..1a5006806b46 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
@@ -1845,6 +1845,14 @@ static int i40e_get_coalesce(struct net_device *netdev,
 
 	ec->rx_coalesce_usecs = vsi->rx_itr_setting & ~I40E_ITR_DYNAMIC;
 	ec->tx_coalesce_usecs = vsi->tx_itr_setting & ~I40E_ITR_DYNAMIC;
+	/* we use the _usecs_high to store/set the interrupt rate limit
+	 * that the hardware supports, that almost but not quite
+	 * fits the original intent of the ethtool variable,
+	 * the rx_coalesce_usecs_high limits total interrupts
+	 * per second from both tx/rx sources.
+	 */
+	ec->rx_coalesce_usecs_high = vsi->int_rate_limit;
+	ec->tx_coalesce_usecs_high = vsi->int_rate_limit;
 
 	return 0;
 }
@@ -1863,6 +1871,17 @@ static int i40e_set_coalesce(struct net_device *netdev,
 	if (ec->tx_max_coalesced_frames_irq || ec->rx_max_coalesced_frames_irq)
 		vsi->work_limit = ec->tx_max_coalesced_frames_irq;
 
+	/* tx_coalesce_usecs_high is ignored, use rx-usecs-high instead */
+	if (ec->tx_coalesce_usecs_high != vsi->int_rate_limit) {
+		netif_info(pf, drv, netdev, "tx-usecs-high is not used, please program rx-usecs-high\n");
+		return -EINVAL;
+	}
+
+	if (ec->rx_coalesce_usecs_high >= INTRL_REG_TO_USEC(I40E_MAX_INTRL)) {
+		netif_info(pf, drv, netdev, "Invalid value, rx-usecs-high range is 0-235\n");
+		return -EINVAL;
+	}
+
 	vector = vsi->base_vector;
 	if ((ec->rx_coalesce_usecs >= (I40E_MIN_ITR << 1)) &&
 	    (ec->rx_coalesce_usecs <= (I40E_MAX_ITR << 1))) {
@@ -1876,6 +1895,8 @@ static int i40e_set_coalesce(struct net_device *netdev,
 		return -EINVAL;
 	}
 
+	vsi->int_rate_limit = ec->rx_coalesce_usecs_high;
+
 	if ((ec->tx_coalesce_usecs >= (I40E_MIN_ITR << 1)) &&
 	    (ec->tx_coalesce_usecs <= (I40E_MAX_ITR << 1))) {
 		vsi->tx_itr_setting = ec->tx_coalesce_usecs;
@@ -1900,11 +1921,14 @@ static int i40e_set_coalesce(struct net_device *netdev,
 		vsi->tx_itr_setting &= ~I40E_ITR_DYNAMIC;
 
 	for (i = 0; i < vsi->num_q_vectors; i++, vector++) {
+		u16 intrl = INTRL_USEC_TO_REG(vsi->int_rate_limit);
+
 		q_vector = vsi->q_vectors[i];
 		q_vector->rx.itr = ITR_TO_REG(vsi->rx_itr_setting);
 		wr32(hw, I40E_PFINT_ITRN(0, vector - 1), q_vector->rx.itr);
 		q_vector->tx.itr = ITR_TO_REG(vsi->tx_itr_setting);
 		wr32(hw, I40E_PFINT_ITRN(1, vector - 1), q_vector->tx.itr);
+		wr32(hw, I40E_PFINT_RATEN(vector - 1), intrl);
 		i40e_flush(hw);
 	}