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Con Kolivas Returns, With a Desktop-Oriented Linux Scheduler
myvirtualid writes "Con Kolivas has done what he swore never to do: returned to the Linux kernel and written a new — and, according to him — waaay better scheduler for the desktop environment. In fact, BFS appears to outperform existing schedulers right up until one hits a 16-CPU machine, at which point he guesses performance would degrade somewhat. According to Kolivas, BFS 'was designed to be forward looking only, make the most of lower spec machines, and not scale to massive hardware. i.e. [sic] it is a desktop orientated scheduler, with extremely low latencies for excellent interactivity by design rather than 'calculated,' with rigid fairness, nice priority distribution and extreme scalability within normal load levels.'"
Oh yeah, and which other scheduler's, if any, did this guy write?
SD scheduler
Took me a while to figure out what "forward looking" means in this context, since "forward-looking scheduler" doesn't seem to be common terminology, and I assumed he wasn't talking about his grand forward-looking vision for schedulerdom.
Based on some previous arguments he's had, it sounds like he opposes the common heuristic of upping interactive process priority by keeping track of how long processes sleep--- processes that sleep a lot are probably I/O bound, and should get a priority boost so they can run on the (less frequent than for CPU-bound processes) occasions when they're ready. Kolivas wants schedulers to be forward-looking in the sense that they decide how to schedule without looking at process run history, by looking purely at who's ready to run, available timeslices, priorities, etc.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
He means something different by it--- that the scheduler should only look forward, not look back to per-process history in making its scheduling decisions. A common hack/heuristic to improve interactive performance is to boost the priority of processes that sleep a lot, since CPU-bound jobs sleep rarely, while interactive processes sleep a lot. Kolivas think that's a hack that obscures the real problems with interactive performance, and leads to unpredictable performance since it doesn't fix the underlying issues. So wants to design schedulers with good interactive performance that make decisions based purely on the current set of running processes and priorities, and the upcoming timeslices.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
What is that? You don't have the choice of scheduler in your kernel? I'm using the Zen sources, and I get to choose between least half a dozen schedulers, including other settings. I am certain that this scheduler will make it into that patchset, and that I will enable it, as soon as zen-sources-2.6.31 get installed on my system.
After all this is Linux! Not some one-company-one-kernel monoculture!
Any sufficiently advanced intelligence is indistinguishable from stupidity.