To PRI or Not To PRI, That's the question
summary
Software-only dynamic passthrough called VIO prevents device DMA page faults without hardware changes by inserting a shadow available queue and IOPA-snooping to probe every DMA before it happens, pinning only hot pages with selective page locking and switching modes with elastic passthrough based on IOPS. Snoop latency is ~3.5–4.5 µs when pages are resident, ~700 µs to resolve a swapped page; peak throughput is within ~10% of passthrough. Deployed across 300K VMs, reclaims up to the equivalent of 30K VM memory daily without breaking SLOs.
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chapters (10)
- 0:00IO pass through optimization
- 1:21Device pass through challenges
- 3:31Limitations for legacy VMs
- 4:56WayIO and key components
- 7:07Monitoring DMA in WayIO
- 9:59Elastic pass through for balance
- 11:05Upgrade legacy VMs without reboot
- 13:16Locking frequently accessed pages
- 14:25WayIO versus hardware solutions
- 16:32Summary and production