Free Software Linux

"We are working [on] a new I/O scheduler based on CFQ, aiming at improved predictability and fairness of the service, while maintaining the high throughput it already provides," began Fabio Checconi, announcing the BFQ I/O scheduler. "The Budget Fair Queueing (BFQ) scheduler turns the CFQ Round-Robin scheduling policy of time slices into a fair queuing scheduling of sector budgets," he continued, "more precisely, each task is assigned a budget measured in number of sectors instead of amount of time, and budgets are scheduled using a slightly modified version of WF2Q+. The budget assigned to each task varies over time as a function of its behaviour. However, one can set the maximum value of the budget that BFQ can assign to any task." Fabio went on to explain:

Adrian Bunk posted a patch to make Linux IO schedulers a non-modular option, which would require one IO scheduler to be selected at compile time. He suggested, "there isn't any big advantage and doesn't seem to be much usage of modular schedulers." He added that removing the option to make IO schedulers modular would save 2kB on each kernel image. Jens Axboe did not like the patch, "big nack, I use it all the time for testing. Just because you don't happen to use it is not a reason to remove it." When Adrian noted that no distros seemed to be making IO schedulers available as modules, Jens suggested that this was a mistake and quipped, "it's been a long time since I considered a distro .config a benchmark/guideline of any sort."