Re: Linux and Intel's Hyperthreading
nick lidakis said:
> I was looking to replace my 1Ghz P3 and motherboard with a stable, but
> fast mb/cpu combo that was fully supported by a recent linux kernel. I
> was looking a an Intel 845PE motherboard with a 3.0Ghz cpu. My question
> is, how is Hyperthreading supported under linux? Is it a matter of
> enabling SMP in the kernel? Anyone playing with one of these CPU's?
it is supported by default. the system will see double the cpus there
actually are. the kernel isn't tuned to fully take advantage of the
hyperthreading yet though. I think newer 2.5.x kernels can do it, perhaps
theres a patch for 2.4.x.. but last I read the current breed of stable
kernels are not optimized for it.
If I had a system with hyperthreading I would disable the hyperthreading
in the bios(one mailing list thread mentioned there is an option to do
so, at least on some systems). Because the kernel would get confused and
think there are 4 processors on a 2 processor system it might try to get
smart by loading stuff up on processor #2, not knowing its the same physical
processor as #1, before loading stuff on #3. I don't remember any benchmark
numbers but I seem to recall there being very little if any difference
in performance on hyperthreaded systems with hyperthreading on vs. off
on the stock kernels(performance can go way up on the newer 2.5.x which
are tuned to take advantage of it in some cases).
I've read one post on the redhat list recently, some guy was asking why
top showed 4 cpus on his dual p4, since it was a dual cpu system, a guy
responded because it was hyperthreading .......
so it should work, just not very optimal.
nate
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