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ixgbe: enable extremely low latency

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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: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jesse Brandeburg 2010-04-27 01:37:20 +00:00 committed by David S. Miller
parent ec857fd40d
commit f8d1dcaf88
2 changed files with 87 additions and 9 deletions
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87
drivers/net/ixgbe/ixgbe_ethtool.c
View File

@ -2079,6 +2079,27 @@ static int ixgbe_get_coalesce(struct net_device *netdev,
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,
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;
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 */
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))
return -EINVAL;
/* check the old value and enable RSC if necessary */
ixgbe_reenable_rsc(adapter, ec);
/* store the value in ints/second */
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 */
adapter->rx_itr_setting &= ~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 */
adapter->rx_eitr_param = 20000;
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
* 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;
/*
* 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) {
/*
* don't have to worry about max_int as above because
* tx vectors don't do hardware RSC (an rx function)
*/
/* check the limits */
if ((1000000/ec->tx_coalesce_usecs > IXGBE_MAX_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);
/* if state changes we need to update adapter->flags and reset */
if ((!!(data & ETH_FLAG_LRO)) !=
(!!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED))) {
adapter->flags2 ^= IXGBE_FLAG2_RSC_ENABLED;
need_reset = true;
if (adapter->flags2 & IXGBE_FLAG2_RSC_CAPABLE) {
/*
* 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;
switch (adapter->hw.mac.type) {
case ixgbe_mac_82599EB:
need_reset = true;
break;
default:
break;
}
} else if (!adapter->rx_itr_setting) {
netdev->features &= ~ETH_FLAG_LRO;
}
}
/*

9
drivers/net/ixgbe/ixgbe_main.c
View File

@ -1189,6 +1189,15 @@ void ixgbe_write_eitr(struct ixgbe_q_vector *q_vector)
/* must write high and low 16 bits to reset counter */
itr_reg |= (itr_reg << 16);
} 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
* immediate assertion of the interrupt