Comment 626 for bug 620074

By moving to BFS, it has been proven (empirically) that IT IS a CPU scheduler issue and not a slow-rotational media problem. Kernel can do other stuff when the rotational media is not giving it what it wants. And don't let buffers and caches fill so much (again a scheduling issue) that even the kernel does not have free pages to run its own components from. All that kernel is doing is spinning finding free pages all the time (kswapd hogging CPU searching through millions of pages on modern systems). Why does it not evict caches by default sooner is not clear? You need to set a bunch of proc parameters for it to start doing that. And it still eventually keels over.

There was a bug reported by someone (and I linked it above) where just pumping network traffic through Linux kernel brought it to its knees leading to cluster reboot. The kernel space (SIRQs) hogged so much CPU during the network traffic processing that user space never got any chance to run. The person moved to BFS and he could run network traffic as fast as he could without bringing anything to its knees. If this is not CPU scheduler issue, then I don't what is!