Linux 6.4 Delivers A Big Performance Boost For VDUSE

Written by Michael Larabel in Linux Kernel on 1 May 2023 at 06:38 AM EDT. 4 Comments
Merged last week for the Linux 6.4 kernel were all of the VirtIO and Virtual Data Path Acceleration (VDPA) changes. Interesting from that pull request is delivering a big performance bump for VDUSE.

For those that don't recall, VDUSE was merged to the kernel back in 2021 with Linux 5.15. VDUSE is around implementing VDPA devices in user-space. The vDPA framework is the VirtIO Data Path Acceleration code within the kernel for devices complying with the VirtIO specification but relying on a vendor-specific control path. The vDPA framework is increasingly used for abstracting hardware and concealing some elements of the hardware complexities to software while having a unified user-space API as a VirtIO device. VDUSE allows for implementing vDPA software-emulated devices in user-space.

Bytedance engineers in the past few months have been working on improving the performance for VDUSE. With a set of patches to mitigate the virtqueue lock contention within the virtio-blk driver, Bytedance is seeing around a 50% performance improvement: from 600k to 900k IOPS in their tests. The patches from Bytedance also add a sysfs interface to allow changing the affinity of IRQ callbacks for each VDUSE virtqueue to help with performance tuning and also a sysfs interface to set the bounce buffer size for virtio-vdpa for tuning with high throughput workloads. The 50% boost alone is nice while these new knobs for further performance tuning is icing on the cake.

The VirtIO/VDPA changes for Linux 6.4 also bring a reduction in the interrupt rate for VirtIO, scalability improvements for vhost-scsi, and other improvements. More details on these changes via this pull.


Those wishing to learn more about VDUSE in general can do so via the documentation.
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