Date: Wed, 7 May 1997 10:04:01 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: steve@visint.co.uk (Stephen Roome) Cc: terry@lambert.org, freebsd-smp@FreeBSD.ORG Subject: Re: Where to start SMP? Message-ID: <199705071704.KAA21345@phaeton.artisoft.com> In-Reply-To: <Pine.BSF.3.91.970507143232.6423F-100000@bagpuss.visint.co.uk> from "Stephen Roome" at May 7, 97 02:37:01 pm
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> > The SMP options also need to be runtime instead of compile time > > configurable, based on flags values which can be modified at boot > > configuration time. This would let a single SMP kernel work on all > > hardware, regardless of which options must be twiddled to get it to > > go. The alternative is multiple "SMP GENERIC" configurations -- not > > a likely event. > > Maybe, but surely some of the changes to run an efficient SMP system > should come at kernel compile level. Unless FreeBSD moves to a modular > system on the scale of something like HURD this looks likely to decrease > performance. Depends on whether the options are set with negative or positive logic, and at what level they are wired in. Best case, they cause the use of different contents of an existing function pointer and are set at boot time. Worst case, they are an extra compare and branch in a path. If you want optimal performance, then have #ifdef's to dike out the compares (worst case) at compile time, and then *you* compile your kernel. The point of a GENERIC is to make some that (within memory limits) works on as much hardware as possible. The same should be true of an SMP-GENERIC, considering it's going to be on a CDROM. > > My suggestion was aimed at main-streaming the code so that there would > > be more feedback, while at the same time offloading some of the issues > > requring hand-holding to the standard UP kernel channels. > > Hand holding gets a user base, don't knock it. It worked for Windows. I understand. But if you can automate it to the level that there isn't a lot of SMP-specific hand-holding, then you've freed up resources to work on SMP. Regards, Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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