From: Alexander Duyck <[email protected]> When operating in latency mode and the computed ITR is lower than the current setting, the algorithm can reduce the interrupt rate too aggressively in a single step. For a TCP workload this means the ACK stream (a latency-sensitive, low-packet-rate workload) can drive the moderation down to very high interrupt rates, starving CPU time from the sender side.
After the speed-based ITR calculation is complete, check whether the result is in latency mode and would decrease below the current setting. If so, limit the decrease to at most IXGBE_ITR_ADAPTIVE_MIN_INC (2 us) per update. This ensures the number of interrupts grows by no more than 2x per adjustment step for latency-class workloads, dialling in smoothly rather than overshooting. Signed-off-by: Alexander Duyck <[email protected]> Reviewed-by: Simon Horman <[email protected]> Signed-off-by: Aleksandr Loktionov <[email protected]> --- drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c index aea76b3..ba7b013 100644 --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c @@ -2888,6 +2888,17 @@ static void ixgbe_update_itr(struct ixgbe_q_vector *q_vector, break; } + /* In the case of a latency specific workload only allow us to + * reduce the ITR by at most 2us. By doing this we should dial + * in so that our number of interrupts is no more than 2x the number + * of packets for the least busy workload. So for example in the case + * of a TCP workload the ACK packets being received would set the + * interrupt rate as they are a latency specific workload. + */ + if ((itr & IXGBE_ITR_ADAPTIVE_LATENCY) && itr < ring_container->itr) + itr = max_t(unsigned int, itr, + ring_container->itr - IXGBE_ITR_ADAPTIVE_MIN_INC); + clear_counts: /* write back value */ ring_container->itr = itr; -- 2.52.0
