Messages in this thread | | | From | Artemio <> | Subject | Re: SMP question | Date | Thu, 12 Jun 2003 08:37:40 +0300 |
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Hello!
Thanks for your reply!
> > Hmmm... So, you mean uni-processor Linux kernel can't see two processors > > as one "big" processor? > > No, but it will work as if it does...explain below. > > You have 2 processor packages, each one is HyperThreading capable. This > means you have two 'CPUs' inside each package, so that sums up your 4 CPUs. > But there is a flaw. The 2 'CPUs' inside each processor package are not > full real CPUs, just two register sets that share cache, FP units, integer > units and so on. So let's say your Xeon has 8 FP units, and you want to > run a FPU intensive task with low or null disk IO. If you activate > hyperthreading each of the 2 'cpus' has 4 FP units, so half the computation > power. If you deactivate HT, you have 1 CPU with 8 FP units. > > In short, for FP intensive tasks, hyperthreading is a big lie... > You can't run 2 computations in parallel.
Thanks for such in-depth explanation!
As I understood, with HT enabled, Linux-SMP sees four CPUs with 5000 bogo mips each (of course I've already seen this in /proc/cpuinfo).
So, if I deactivate HT, will a UP Linux see one CPU with 4x5000=20000 bogo mips?
Anyway, I will try what I mentioned on that machine today.
Thank you again and good luck!
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