# Experimental sync queues cut VirtIO-FS build times by 28%

> **Key takeaway:** Pending synchronous queue support for VirtIO-FS reduced a libkrunfw build from 7:43 to 5:34 in testing by Sergio López.

**Published:** 2026-10-18T00:55:35+00:00 
**Source:** Phoronix Benchmarks & Drivers 
**Category:** kernel-os 
**Canonical URL:** https://fosswire.org/news/experimental-sync-queues-cut-virtio-fs-build-times-by-28.html 

## Summary
Sergio López has developed experimental synchronous queue support for VirtIO-FS, the paravirtualized filesystem used for host-guest VM data transfers. Unlike VirtIO's typical asynchronous model, synchronous queues let the host vCPU thread complete I/O requests before returning to the guest. Testing showed a libkrunfw build time drop from 7 minutes 43 seconds to 5 minutes 34 seconds, alongside improvements in random I/O and file deletion latency. The work is available as a pending pull request for libkrun with optional VIRTIO_FS_F_SYNC support.

## How synchronous queues change VirtIO-FS behavior
- **Default VirtIO model**: asynchronous queues where the guest continues execution without waiting for host I/O completion
- **Sync queue mechanism**: host vCPU thread blocks and completes the filesystem request before returning control to guest
- **Measured workload**: libkrunfw build time reduced from **7:43 to 5:34** (~28% improvement)
- **Additional gains**: significant random I/O performance improvement and lower file deletion latency
- **Implementation status**: experimental pull request for libkrun adding optional `VIRTIO_FS_F_SYNC` flag support

## Why it matters
If merged, this could substantially improve I/O-bound workload performance for cloud VMs and container sandboxes using VirtIO-FS, particularly for compilation and build scenarios where synchronous completion is already effectively required.