Data Sheet

Inline Functions—Ethernet Controller I210
331
7.3.6 Rate Controlled Low Latency Interrupts (LLI)
There are some types of network traffic for which latency is a critical issue. For these types of traffic,
interrupt moderation hurts performance by increasing latency between the time a packet is received by
hardware and the time it is handled to the host operating system. This traffic can be identified by the 2-
tuple value, in conjunction with Control Bits and specific size. In addition packets with specific Ethernet
types, TCP flag or specific VLAN priority might generate an immediate interrupt.
Low latency interrupts shares the filters used by the queueing mechanism described in Section 7.1.1.
Each of these filters, in addition to the queueing action might also indicate matching packets might
generate immediate interrupt.
If a received packet matches one of these filters, hardware should interrupt immediately, overriding the
interrupt moderation by the EITR counter.
Each time a Low Latency Interrupt is fired, the EITR interval is loaded and down-counting starts again.
The logic of the low latency interrupt mechanism is as follows:
• There are 8 2-tuple filters. The content of each filter is described in Section 7.1.2.4. The immediate
interrupt action of each filter can be enabled or disabled. If one of the filters detects an adequate
packet, an immediate interrupt is issued.
Figure 7-16. Case A: Heavy Load, Interrupts Moderated
Figure 7-17. Light load, Interrupts Immediately on Packet Receive
Pkt Pkt Pkt Pkt Pkt Pkt
ITR delay ITR delay
Intr
Intr Intr
Pkt Pkt
EICR
clear
EICR
clear
EICR
clear
Pkt Pkt
ITR delay
Intr
Intr
EICR
clear
EICR
clear