4 ms·

Also, I've been thinking on what you've written about cooperative multitasking OS'es and why preemptive concurrency took over. Cooperative multitasking is easi

• btilly 10y ago
  There is that. And the fact that it is straightforward to extend an existing preemptive system to handle multiple CPUs, but not obvious how to do it with cooperative ones. That said, there are many possible trade-offs between preemption and cooperation. It is old, but http://www.bitmover.com/llnl/smp.pdf http://www.bitmover.com/llnl/smp.pdf made a good case for why SMP was the wrong way to scale to large numbers of CPUs. NUMA is a much better architecture. SGI demonstrated this in the 1990s with 1000 CPU machines. Unfortunately Linux took the SMP path like Solaris before it, and our performance is suffering as a result. :-( An interesting historical note. Larry McVoy's thinking about how to handle contention lead him to thinking about a very, very slowed down version of it - distributed source control. This lead to a "side project" named BitKeeper. Move a few years later and that was a real product used for the Linux kernel. After some drama, he withdrew permission for Linux to continue using it for free and in response Linus wrote git. (Linus and Larry were always on good terms. The drama was between Larry and Jeremy Allison, of SAMBA fame.)