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Fast path to me has always meant no software that runs on a general purpose CPU. It means the packet needs to traverse the device without being touched by softw
by AndyMcConachie 10y ago
Fast path to me has always meant no software that runs on a general purpose CPU. It means the packet needs to traverse the device without being touched by software that runs on a general purpose CPU. ASIC or similar only.
The minute we start talking about fast-path in-kernel is when I realize that Linux folks and most networking folk who use the term have a different idea of what fast-path means. Still interesting, but not what I thought I would be reading.
- woah 10y agoDo most routers have ASICs that read the routing table then?
- AndyMcConachie 10y agoI don't know why you were downvoted, this is a good question. Yes. The terms used in BGP are typically Router Information Base (RIB) and Forwarding Information Base (FIB). Generally speaking the FIB is stored in some type of memory that has a fixed lookup time and does not involve a general purpose CPU.
- ky3 10y agoA case of only so many words in the English language. Easy to fix if we distinguish hardware fast path from the software variant. Software fast paths are worth looking into since context switches are costly to the tune of thousands of CPU cycles [0,1]. Those thousands of CPU instructions going up in smoke could've done quite a lot of useful work. [0] http://blog.tsunanet.net/2010/11/how-long-does-it-take-to-make-context.html http://blog.tsunanet.net/2010/11/how-long-does-it-take-to-ma... [1] https://gist.github.com/nelsnelson/3955759 https://gist.github.com/nelsnelson/3955759