1. Network Stack Specialization for Performance
Presented by Donghwi Kim
(Some figures are brought from the paper)

2. Objective
The authors tried to show upper bound of network application performance by specialization (Actually, not only a network stack but also an application’s implementation is specialized)
A special kind of applications is chosen (Serves same content to multiple users)
Sandstorm: A Web server serves static webpage
Namestorm: A DNS server

3. Key of performance A complete zero-copy stack Aggressive amortization
Pre-packetized data
Batching to mitigate system-call overhead
Synchronous, clocked from received packets
Improves cache locality
Minimize the latency of sending the first packet of response
Intel’s DDIO

4. Network stack libnmio: Data-movement and event-notification primitives
libeth: A lightweight Ethernet-layer
libtcpip: An optimized TCP/IP layer
libudpip: A UDP/IP layer

5. A complete zero-copy stack
Receiving a packet
Done by DMA
Transmitting a packet
Aggressive amortization
Modify one of prepared a copy of packet and use DMA
The modifications are performed in a single pass to use CPU’s L1 cache efficiently

6. A complete zero-copy stack
pre-copy method
maintain more than one copy of each packet
potential to thrash CPU’s L3 cache
memcpy method
maintain one long-term copy and create ephemeral copies
more work should be done

7. How the optimization works?
Batching increases TCP RTT
Amortizing reduces per-request processing

8. Intel’s DDIO Direct Data I/O When transmission When reception
Pull data from the L3 cache without a detour through system memory
When reception
DMA can place data in processor’s L3 cache

9. Evaluation

10. Evaluation

11. Evaluation

12. DDIO
Pre-copy case: DDIO pulls untouched incoming data into the cache, so the file data cannot be cached
Memcopy case: CPU loads file data into the cache

13. Discussion
mTCP vs. Sandstorm

14. Discussion mTCP TCP of Sandstorm
Provides UNIX-like socket programming interface
mTCP provides fairness
TCP of Sandstorm
Higher level stack does not wrap lower level stack
Each stack is a stand-alone service
For example, an application interacts directly with libnmio
Amortization, no-queueing, inaccurate timer cannot guarantee correctness
Limited applications