Hyper Threading on the E5-2696v3

I just did some quick tests of hyper-threading on my new E5-2696v3 CPU. I compiled the Linux 6.0.10 kernel with and without hyper-threading enabled. Here’s the times for “make -j36 bzImage” and “make -j36 modules” with HT enabled:

real    2m26.540s
user    55m25.121s
sys     9m56.443s

real    10m57.374s
user    309m21.531s
sys     58m1.070s

Here’s the times for “make -j18 bzImage” and “make -j18 modules” with HT disabled:

real    2m40.501s
user    31m35.295s
sys     5m43.523s

real    11m39.313s
user    170m46.840s
sys     31m37.756s

That’s 9.6% faster for bzImage and 6.4% faster for modules.

So for a performance boost that’s between 5% and 10% I get greater exposure to kernel security issues and more difficulty tracking CPU time. That doesn’t seem like a good trade-off so I’ve put the “nosmt” kernel command-line option back.