On 04/13/2013 01:45 PM, Pandu Poluan wrote: > [snip] > Three, AMD has no concept of Hyperthreading.
Correct. > Just match -j to the number of cores your CPU provides, and that's > it. Well, YMMV. You can spend a lot of time adjusting -j on a per-system basis to account for things like I/O. Right now, I'm in the "-j $(cores*1.5) -l $(cores)" camp. > > As I wrote, an AMD Quad Core provides actual 4 cores. Correct. > An "Intel Quad Core with Hyperthreading" actually provides only 2 > physical cores, but then it performs some internal trickery so the OS > sees a total of 4 cores. Incorrect. Intel Quad Core with Hyperthreading means there are four physical cores, and there is hyperthreading enabled. This results in the OS seeing eight logical cores. There is sufficient information available via ACPI (or is it DMI?) that the kernel knows which virtual cores are part of which physical cores, which physical cores are part of which CPU packages, and how everything is connected together. > > I much prefer having 4 actual cores than 4 virtual cores (only 2 > actual cores); less chance of things messing up royally if I hit some > edge cases where Hyperthreading falls flat on its face. Whatever works. I'll note that AMD's piledriver core does something very complementary to hyperthreading. Where HT uses some circuitry to avoid context switching when changing whether a core is handling one thread vs another thread, Piledriver has a small number of physical front-end cores dispatching to a larger number of backend pipelines. It's a very curious architecture, and I look forward to seeing how it plays out. HT and Piledriver are conceptually very similar when you look at them in the right way...Piledriver might be seen as a more general approach to what HT does. Personally, I've enjoyed both Intel and AMD processors. Last I assembled a system, Intel's midrange offered more bang for the buck than AMD, but Intel's midrange part was also much more expensive. OTOH, AMD systems could be upgraded for piece by piece for much, much, much longer, whereas Intel systems tended to require replacing many more parts at the same time. That was about five years ago, though...I don't know exactly where things sit today. I'd start with the cpubenchmarking.net CPU value listing, and find the best-value part that has the performance degree I'm looking for. http://cpubenchmark.net/cpu_value_available.html I might also cross-reference that page with this one: http://cpubenchmark.net/mid_range_cpus.html If buying an Intel part, I'd be very, very careful to make sure that it supported all the features I want. I've been bit by that on this laptop...I had no idea it wouldn't have VT-x.
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