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Commit f8d1dcaf authored by Jesse Brandeburg's avatar Jesse Brandeburg Committed by David S. Miller
Browse files

ixgbe: enable extremely low latency 



82598/82599 can support EITR == 0, which allows for the
absolutely lowest latency setting in the hardware.  This disables
writeback batching and anything else that relies upon a delayed
interrupt. This patch enables the feature of "override" when a
user sets rx-usecs to zero, the driver will respect that setting
over using RSC, and automatically disable RSC.  If rx-usecs is
used to set the EITR value to 0, then the driver should disable
LRO (aka RSC) internally until EITR is set to non-zero again.

Signed-off-by: default avatarJesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ec857fd4

drivers/net/ixgbe/ixgbe_ethtool.c

+78 −9
Original line number Original line Diff line number Diff line
@@ -2079,6 +2079,27 @@ static int ixgbe_get_coalesce(struct net_device *netdev, 
	return 0;

	return 0;

}

}





/*

 * this function must be called before setting the new value of

 * rx_itr_setting

 */

static void ixgbe_reenable_rsc(struct ixgbe_adapter *adapter,

                               struct ethtool_coalesce *ec)

{

	/* check the old value and enable RSC if necessary */

	if ((adapter->rx_itr_setting == 0) &&

	    (adapter->flags2 & IXGBE_FLAG2_RSC_CAPABLE)) {

		adapter->flags2 |= IXGBE_FLAG2_RSC_ENABLED;

		adapter->netdev->features |= NETIF_F_LRO;

		DPRINTK(PROBE, INFO, "rx-usecs set to %d, re-enabling RSC\n",

		        ec->rx_coalesce_usecs);

		if (netif_running(adapter->netdev))

			ixgbe_reinit_locked(adapter);

		else

			ixgbe_reset(adapter);

	}

}



static int ixgbe_set_coalesce(struct net_device *netdev,

static int ixgbe_set_coalesce(struct net_device *netdev,

                              struct ethtool_coalesce *ec)

                              struct ethtool_coalesce *ec)

{

{
@@ -2095,11 +2116,20 @@ static int ixgbe_set_coalesce(struct net_device *netdev, 
		adapter->tx_ring[0]->work_limit = ec->tx_max_coalesced_frames_irq;

		adapter->tx_ring[0]->work_limit = ec->tx_max_coalesced_frames_irq;





	if (ec->rx_coalesce_usecs > 1) {

	if (ec->rx_coalesce_usecs > 1) {

		u32 max_int;

		if (adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED)

			max_int = IXGBE_MAX_RSC_INT_RATE;

		else

			max_int = IXGBE_MAX_INT_RATE;



		/* check the limits */

		/* check the limits */

		if ((1000000/ec->rx_coalesce_usecs > IXGBE_MAX_INT_RATE) ||

		if ((1000000/ec->rx_coalesce_usecs > max_int) ||

		    (1000000/ec->rx_coalesce_usecs < IXGBE_MIN_INT_RATE))

		    (1000000/ec->rx_coalesce_usecs < IXGBE_MIN_INT_RATE))

			return -EINVAL;

			return -EINVAL;





		/* check the old value and enable RSC if necessary */

		ixgbe_reenable_rsc(adapter, ec);



		/* store the value in ints/second */

		/* store the value in ints/second */

		adapter->rx_eitr_param = 1000000/ec->rx_coalesce_usecs;

		adapter->rx_eitr_param = 1000000/ec->rx_coalesce_usecs;
@@ -2108,6 +2138,9 @@ static int ixgbe_set_coalesce(struct net_device *netdev, 
		/* clear the lower bit as its used for dynamic state */

		/* clear the lower bit as its used for dynamic state */

		adapter->rx_itr_setting &= ~1;

		adapter->rx_itr_setting &= ~1;

	} else if (ec->rx_coalesce_usecs == 1) {

	} else if (ec->rx_coalesce_usecs == 1) {

		/* check the old value and enable RSC if necessary */

		ixgbe_reenable_rsc(adapter, ec);



		/* 1 means dynamic mode */

		/* 1 means dynamic mode */

		adapter->rx_eitr_param = 20000;

		adapter->rx_eitr_param = 20000;

		adapter->rx_itr_setting = 1;

		adapter->rx_itr_setting = 1;
@@ -2116,14 +2149,34 @@ static int ixgbe_set_coalesce(struct net_device *netdev, 
		 * any other value means disable eitr, which is best

		 * any other value means disable eitr, which is best

		 * served by setting the interrupt rate very high

		 * served by setting the interrupt rate very high

		 */

		 */

		if (adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED)

			adapter->rx_eitr_param = IXGBE_MAX_RSC_INT_RATE;

		else

		adapter->rx_eitr_param = IXGBE_MAX_INT_RATE;

		adapter->rx_eitr_param = IXGBE_MAX_INT_RATE;

		adapter->rx_itr_setting = 0;

		adapter->rx_itr_setting = 0;



		/*

		 * if hardware RSC is enabled, disable it when

		 * setting low latency mode, to avoid errata, assuming

		 * that when the user set low latency mode they want

		 * it at the cost of anything else

		 */

		if (adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) {

			adapter->flags2 &= ~IXGBE_FLAG2_RSC_ENABLED;

			netdev->features &= ~NETIF_F_LRO;

			DPRINTK(PROBE, INFO,

			        "rx-usecs set to 0, disabling RSC\n");



			if (netif_running(netdev))

				ixgbe_reinit_locked(adapter);

			else

				ixgbe_reset(adapter);

			return 0;

		}

	}

	}





	if (ec->tx_coalesce_usecs > 1) {

	if (ec->tx_coalesce_usecs > 1) {

		/*

		 * don't have to worry about max_int as above because

		 * tx vectors don't do hardware RSC (an rx function)

		 */

		/* check the limits */

		/* check the limits */

		if ((1000000/ec->tx_coalesce_usecs > IXGBE_MAX_INT_RATE) ||

		if ((1000000/ec->tx_coalesce_usecs > IXGBE_MAX_INT_RATE) ||

		    (1000000/ec->tx_coalesce_usecs < IXGBE_MIN_INT_RATE))

		    (1000000/ec->tx_coalesce_usecs < IXGBE_MIN_INT_RATE))
@@ -2178,10 +2231,26 @@ static int ixgbe_set_flags(struct net_device *netdev, u32 data) 
	ethtool_op_set_flags(netdev, data);

	ethtool_op_set_flags(netdev, data);





	/* if state changes we need to update adapter->flags and reset */

	/* if state changes we need to update adapter->flags and reset */

	if ((!!(data & ETH_FLAG_LRO)) != 

	if (adapter->flags2 & IXGBE_FLAG2_RSC_CAPABLE) {

	    (!!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED))) {

		/*

		 * cast both to bool and verify if they are set the same

		 * but only enable RSC if itr is non-zero, as

		 * itr=0 and RSC are mutually exclusive

		 */

		if (((!!(data & ETH_FLAG_LRO)) !=

		     (!!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED))) &&

		    adapter->rx_itr_setting) {

			adapter->flags2 ^= IXGBE_FLAG2_RSC_ENABLED;

			adapter->flags2 ^= IXGBE_FLAG2_RSC_ENABLED;

			switch (adapter->hw.mac.type) {

			case ixgbe_mac_82599EB:

				need_reset = true;

				need_reset = true;

				break;

			default:

				break;

			}

		} else if (!adapter->rx_itr_setting) {

			netdev->features &= ~ETH_FLAG_LRO;

		}

	}

	}





	/*

	/*

drivers/net/ixgbe/ixgbe_main.c

+9 −0
Original line number Original line Diff line number Diff line
@@ -1189,6 +1189,15 @@ void ixgbe_write_eitr(struct ixgbe_q_vector *q_vector) 
		/* must write high and low 16 bits to reset counter */

		/* must write high and low 16 bits to reset counter */

		itr_reg |= (itr_reg << 16);

		itr_reg |= (itr_reg << 16);

	} else if (adapter->hw.mac.type == ixgbe_mac_82599EB) {

	} else if (adapter->hw.mac.type == ixgbe_mac_82599EB) {

		/*

		 * 82599 can support a value of zero, so allow it for

		 * max interrupt rate, but there is an errata where it can

		 * not be zero with RSC

		 */

		if (itr_reg == 8 &&

		    !(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED))

			itr_reg = 0;



		/*

		/*

		 * set the WDIS bit to not clear the timer bits and cause an

		 * set the WDIS bit to not clear the timer bits and cause an

		 * immediate assertion of the interrupt

		 * immediate assertion of the interrupt