Hi everyone! We experimented with the BPF patchset provided by Pavel a few months ago. And I had the exact same question: How can we compare the benefits and drawbacks of a more flexible io_uring implementation? In that specific use case, I wanted to show that a flexible SQE-dependency generation with BPF could outperform user-space SQE scheduling. From my experience with BPF, I learned that it is quite hard to beat io_uring+userspace, if there is enough parallelism in your IO jobs. For this purpose, I've built a benchmark generator that is able to produce random dependency graphs of various shapes (isolated nodes, binary tree, parallel-dependency chains, random DAC) and different scheduling backends (usual system-call backend, plain io_uring, BPF-enhanced io_uring) and different workloads. At this point, I didn't have the time to polish the generator and publish it, but I put the current state into this git: https://collaborating.tuhh.de/e-exk4/projects/syscall-graph-generator After running: ./generate.sh [sudo modprobe null_blk...] ./run.sh ./analyze.py You get the following results (at least if you own my machine): generator iouring syscall iouring_norm graph action size chain read 128 938.563366 2019.199010 46.48% flat read 128 922.132673 2011.566337 45.84% graph read 128 1129.017822 2021.905941 55.84% rope read 128 2051.763366 2014.563366 101.85% tree read 128 1049.427723 2015.254455 52.07% For the userspace scheduler, I perform an offline analysis that finds linear chains of operations that are not (anymore) dependent on other previous unfinished results. These linear chains are then pushed into io_uring with a SQE-link chain. As I'm highly interested in this topic of pushing complex IO-dependencies into the kernel space, I would be delighted to see how your SQE-graph extension would compare against my rudimentary userspace scheduler. @Hao: Do you have a specific use case for your graph-like dependencies in mind? If you need assistance with the generator, please feel free to contact me. chris -- Prof. Dr.-Ing. Christian Dietrich Operating System Group (E-EXK4) Technische Universität Hamburg Am Schwarzenberg-Campus 3 (E), 4.092 21073 Hamburg eMail: christian.dietrich@xxxxxxx Tel: +49 40 42878 2188 WWW: https://osg.tuhh.de/
