- Must avoid operating system overhead:
- Run RAMCloud as part of the kernel?
- "Use the cores, Luke": dedicate one core to managing the network, don't take interrupts?
- What is the right network protocol?
- TCP flow control and retry don't seem appropriate for operation within a datacenter.
- Some data on switch latency from Brandon Heller:
The datasheet quotes 200ns for the L2-only FM2000, 300ms with ACLs enabled for the FM3000. Arista quotes 600ns delay regardless of packet size for their 24-port switches and 1200ns for their 48p version, which uses an internal fat tree of 6 24p FocalPoint chips (so 3 300ns hops are req'd).
The PHY can also add quite a bit of delay; supposedly 10GBase-T transceivers, due to the block encode/decode delay, add 1us per link (Wikipedia). Fiber, CX4, and twinax should be much lower-latency, since they escrew the fancy coding techniques for lower-error cabling. This is something I'd like to measure with the Triumph box coming soon.
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