Io_uring, kTLS and Rust for zero syscall HTTPS server

Your write up connected some early knowledge from when I was 11 where I was trying to set up a database/backend and was finding lots of cgi-bin online. I realize now those were spinning up new processes with each request https://en.wikipedia.org/wiki/Common_Gateway_Interface

I remember when sendfile became available for my large gaming forum with dozens of TB of demo downloads. That alone was huge for concurrency.

I thought I had swore off this type of engineering but between this, the Netflix case of extra 40ms and the GTA 5 70% load time reduction maybe there is a lot more impactful work to be done.

https://netflixtechblog.com/life-of-a-netflix-partner-engine...

https://nee.lv/2021/02/28/How-I-cut-GTA-Online-loading-times...

Depends on the workload.

Normally you would go read() -> write() so:

1. Disk -> page cache (DMA)

2. Kernel -> user copy (read)

3. User -> kernel copy (write)

4. Kernel -> NIC (DMA)

sendfile():

1. Disk -> page cache (DMA)

No user space copies, kernel wires those pages straight to the socket

2. Kernel -> NIC (DMA)

So basically, it eliminates 1-2 memory copies along with the associated cache pollution and memory bandwidth overhead. If you are running high QPS web services where syscall and copy overheads dominate, for example CDNs/static file serving the gains can be really big. Based on my observations this can mean double digit reductions in CPU usage and up to ~2x higher throughput.