Messages in this thread | | | Date | Wed, 20 Jun 2001 14:35:25 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: Alan Cox quote? (was: Re: accounting for threads) |
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On Wed, 20 Jun 2001, george anzinger wrote:
> > around we _will_ get problems. Kernel UP programming is not different > > from SMP one. It is multithreaded. And amount of genuine SMP bugs is > > very small compared to ones that had been there on UP since way back. > > And yes, programming threads is the same thing. No arguments here. > > > Correct, IF the UP kernel is preemptable. As long as it is not (and SMP > is ignored) threads are harder BECAUSE they are preemptable.
In practice it's a BS. There is a lot of ways minor modifications of code could add a preemption point, so if you rely on the lack of such - expect major PITA.
Yes, in theory SMP adds some extra fun. Practically, almost every "SMP" race found so far did not require SMP.
Clean code is trivial to make SMP-safe - critical areas that rely on lack of preemption are couple of instructions wide and are easy to protect. Anything trickier and I bet that you have a race on (normal) UP kernel. Been there, found probably several hundreds of them.
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