CVM-IO Motivation

[enterJazz]

Motivate CVM IO

• Bifrost: VM_EXITs and BB tax
• Performance Overheads of Confidential Virtual
  Machines:

Disk I/O from CVMs experiences the worst performance impact, with up to 56% overhead, while network I/O experiences up to 36% overhead.

• own eval results: SEV + TDX
  

[enterJazz]

ISSUE

Project does currently NOT convince Pramod.

As discussed w/ Peter and @mmisono , the current 'lack' of overhead gap is due to virtio-blk backend use.

• as shown in Spool: major differences in virtio-blk and SPDK performance!
  
• virtio-blk is presumably a botteleneck when it comes to performance differences
  • hence: performance differences are being watered out!

ISSUE:

• we can't directly compare native VM w/ SPDK and CVM w/ SPDK
  • we can't confirm bottleneck in this way

INSTEAD:
We can either:
i. do measurements to show that virtio-blk is indeed taking up most of the performance
ii. or: compare virito-blk w/ spdk directly -> argue that perf difference shows bottleneck

either i or ii, we need to show that CVM drawbacks make a large difference when SPDK is used

[enterJazz]

@mmisono

I reran swiotlb benchmarks w/ native (unmodified, diff branch) kernel, to ensure we didn't make a mistake.
Saw minimal perf difference, so current measurements are correct.