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 sw2SmywA 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It's not even close to >>> correct, but it builds, boots and survives lightweight testing. >> >> Whew, that was electric. I had barely managed to sort through some of >> the config maze. >> From a quick look this is pretty much how you described it. > > Unsurpringly I spent at least 10x the time to describe it than to hack > it up. > > IOW, I had done the analysis before I offered the idea and before I > changed a single line of code. The tools I used for that are git-grep, > tags, paper, pencil, accrued knowledge and patience, i.e. nothing even > close to rocket science. > > Converting the analysis into code was mostly a matter of brain dumping > the analysis and adherence to accrued methodology. > > What's electric about that? Hmm, so I /think/ I was going for something like electric current taking the optimal path, with a side meaning of electrifying. Though, I guess electron flow is a quantum mechanical, so that would really try all possible paths, which means the analogy doesn't quite fit. Let me substitute greased lightning for electric :D. > I might be missing some meaning of 'electric' which is not covered by my > mostly Webster restricted old-school understanding of the english language :) > >>> I did not even try to look into time-slice enforcement, but I really want >>> to share this for illustration and for others to experiment. >>> >>> This keeps all the existing mechanisms in place and introduces a new >>> config knob in the preemption model Kconfig switch: PREEMPT_AUTO >>> >>> If selected it builds a CONFIG_PREEMPT kernel, which disables the >>> cond_resched() machinery and switches the fair scheduler class to use >>> the NEED_PREEMPT_LAZY bit by default, i.e. it should be pretty close to >>> the preempt NONE model except that cond_resched() is a NOOP and I did >>> not validate the time-slice enforcement. The latter should be a >>> no-brainer to figure out and fix if required. >> >> Yeah, let me try this out. > > That's what I hoped for :) :). Quick update: it hasn't eaten my hard disk yet. Both the "none" and "full" variants are stable with kbuild. Next: time-slice validation, any fixes and then maybe alarm-clock deployments. And, then if you are okay with it, I'll cleanup/structure your patches together with all the other preemption cleanups we discussed into an RFC series. (One thing I can't wait to measure is how many cond_resched() calls and associated dynamic instructions do we not execute now. Not because I think it really matters for performance -- though it might on low IPC archs, but just it'll be a relief seeing the cond_resched() gone for real.) -- ankur