Ingo Molnar Tests New BF Scheduler

Ingo Molnar wasn't quite ready to accept criticism of the performance of his scheduler currently in the kernel compared to the BFS version and put them both to a benchmark test. In his posting he admits that BFS is still in its early stages, but finds Kolivas's code fascinating: "BFS is an interesting and bold new approach, cutting a _lot_ of code out of kernel/sched*.c, so it raised my curiosity and interest."

Because Kolivas set the limit to 16 CPUs, Molnar put BFS on a system with dual quad core and hyperthreading. The result is that he couldn't see "any BFS performance improvements, on this box." In fact, he claimed that BFS failed in comparison in almost all cases, including kernel build, pipe, messaging and OLTP performance. "In the kbuild test BFS is showing significant weaknesses up to 16 CPUs. On 8 CPUs utilized (half load) it's 27.6% slower."

The CFS developer nonetheless had a few positive things to say about BFS: "General interactivity of BFS seemed good to me -- except for the pipe test when there was significant lag over a minute. I think it's some starvation bug, not an inherent design property of BFS, so I'm looking forward to retest it with the fix." He encouraged others to repeat his tests.

Molnar's posting is comprehensive in his test description, listing the links to his tests and providing detailed results. Beside the passion for scheduler development, he finds a few more things in common with the Australian, as he said to him: "I'd like to outline that I agree with the general goals described by you in the BFS announcement -- small desktop systems matter more than large systems." He therefore bade Kolivas to work together with him, ending with, "we'll also be following BFS for good ideas and code to adopt to mainline."

The Hungarian developer working for Red Hat programmed the Completely Fair Scheduler currently used in the Linux kernel. Kolivas had recently broken a two-year Linux hiatus to develop BFS in response to what he felt was CFS's inability to fully utilize the CPU.