Miguel Bazdresch wrote: > I agree with all you say, but I believe you're missing something more > important than context switches: cache and bus conflicts. These are > the main reason performance suffers when a core is running more than > one active thread.
Right, I kind of assumed that stuff was part of the context-switch overhead. The cache wouldn't need to flush (and wouldn't suddenly be filled with useless data, which is effectively the same thing) if the same physical addresses were coming from the CPU; once the CPU starts running another process, those physical addresses will all start changing. OTOH, by your numbers, overall performance (at least on binutils) doesn't suffer until you get to 4 jobs on the 2 cores. And even then, it's a fairly small difference. Well, whatever. I like Dan's idea, FWIW (mention the -j option in the text, but put a cautionary note in there saying that compile errors may happen, and to re-try the compile without -j if they do).
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