Date: Mon, 08 Nov 2004 13:11:04 -0800 From: Julian Elischer <julian@elischer.org> To: Robert Watson <rwatson@freebsd.org> Cc: julian@freebsd.org Subject: Re: preemption stable under 5.3? Message-ID: <418FE0E8.1020702@elischer.org> In-Reply-To: <Pine.NEB.3.96L.1041108182215.73102M-100000@fledge.watson.org> References: <Pine.NEB.3.96L.1041108182215.73102M-100000@fledge.watson.org>
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Robert Watson wrote: >On Mon, 8 Nov 2004, Mipam wrote: > > > >>Thanks for your reply, okay, then i'd like to enable preemption. I >>noticed it's not in the GENERIC kernel config file. So: options >>PREEMPTION would suffice to enable it i guess? Any experience with >>preemption. noticable changes? So the problem: "PREEMPTION triggers >>frequent hangs" is resolved? Btw, is RELENG_5 also stable or only for >>early adopters? I really would like to see ule working stable in >>combination with preemption, but in 5.3 it won't happen. Maybe ule will >>be enabled later in the 5 series? >> >> > >There was a series of bugs in the scheduler which got tickled by >preemption; I'm unclear as to whether they were all resolved before 5.3 or >whether they require fixes in HEAD that haven't yet been merged. It may >well be safe, but I make no promises. Hopefully we can trick Julian or >John into responding to this thread. :-) Having it off by default on 5.3 >is certainly the more conservative (and reasonable) position, but if it >helps your environment and appears stable, there should be no reason not >to turn it on. It should substantially improve latency in interrupt >processing as well as packet processing. > I think that PREEMPTION with SCHED_4BSD might be ok.. It's hard to say because it's always harder to prove something correct than to prove it broken :-) Hopefully with the rush off, we can sit down and try "prove it ok" and take some cleanup passes over it. I still owe my wife a significant "chunk-o-time" (TM) however so count me out for a while . Hopefully however ups@ is coming online again this week.
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