# VirtIO-FS synchronous queues cut build times by 28% in tests

> **Key takeaway:** Experimental synchronous queue support for VirtIO-FS reduced a libkrunfw build from 7:43 to 5:34 and improved random I/O and file deletion latency.

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

## Summary
Sergio López has developed experimental synchronous queue support for VirtIO-FS, the paravirtualized file system used for host-guest VM data transfers. Unlike VirtIO's typical asynchronous model, synchronous queues allow the host vCPU thread to complete I/O requests before returning to the guest. Testing showed a libkrunfw build time reduction from 7 minutes 43 seconds to 5 minutes 34 seconds, alongside gains in random I/O and lower 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 I/O completion
- **Synchronous variant**: host vCPU thread blocks and completes the request before returning control to the guest
- **Measured workload**: libkrunfw build time dropped from **463 seconds to 334 seconds** (28% reduction)
- **Additional gains**: significant random I/O improvement and reduced file deletion latency
- **Implementation status**: experimental pull request for libkrun adding `VIRTIO_FS_F_SYNC` feature flag

## Why it matters
If merged, this could improve VM workload performance broadly for cloud and container platforms using VirtIO-FS, particularly for build and compilation tasks that are I/O latency-sensitive.