IP Forwarding Using Peer DMA

Benefits of Host Based Forwarding

• Programmability
• Commodity Platforms and Network Interfaces
• Network Interface Cards track technology advances
• NICs precede line cards (if line cards exist at all).

Example Uses in research

• in testbeds DARTnet and successor CAIRN
• Active Networks
• ATOMIC project supporting Myrinet LAN at ISI

Problems

• Latency - store and forward copying
• Bandwidth - bus limited bandwidth
• CPU Load - interrupts; cycles to manage transfers (PIO more than DMA)

Solution: Forwarding Using Peer DMA (2 approaches)

• keep packet on NIC
• data on NIC, copy header to host

Results

• UDP throughput up by over 40%
• CPU pegged for small packet sizes and multiple sources
• Relieves CPU load by 35% for 2 sources
• Max packet per sec 12,000 @ 128 byte packet sizes
• Worse for TO-Host traffic (PIO)

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Last modified April, 1998.