How to enable Hyper-threading?

[rmautino]

Hello,

I did an install from Stage one. When I compiled my kernel, I did the genkernel --menuconfig all command. I did verufy that SMP support was there.

Processor type and features --->
[*] Symmetric multi-processing support

When I do dmesg, I see this in the output....

CPU: Hyper-Threading is disabled.


How can I get this going and then verify it is going?

Thanks,
Rob

[rkrenzis]

Could you please provide more information like the version of kernel you are using?

Try emerging "gentoo-dev-sources" and symlink the linux directory to that version.

Select...
[*] Symmetric multi-processing support

Then...

[*] SMT (Hyperthreading) scheduler support

Update your make.conf to include MAKE_OPTS="-j3"

Although HT is not exactly like dual processors it does give you a 30-40% increase versus only having one core.

[rmautino]

Hello,


Sorry. My kernel is gentoo-dev-sources. kernel-2.6.9-gentoo-r13

This is my Make.conf:
CFLAGS="-O2 -march=pentium4 -pipe -fomit-frame-pointer"
CHOST="i686-pc-linux-gnu"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j3"
USE="-gtk -gnome qt kde dvd alsa cdr"


I selected SMP and Hyper-threading support with make menuconfig

Processor type and features ---> Processor type and features --->

[*] Symmetric multi-processing support
(8) Maximum number of CPUs (2-255)
[*] SMT (Hyperthreading) scheduler support


My question is, when I run the command
# dmesg

In the Output I see:

CPU: After generic identify, caps: bfebfbff 00000000 00000000 00000000
CPU: After vendor identify, caps: bfebfbff 00000000 00000000 00000000
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Hyper-Threading is disabled
CPU: After all inits, caps: bfebfbff 00000000 00000000 00000080



Does this actually mean that Hyper threading is disabled?

Thanks,
Rob

[n3mo]

If you want HT enabled you have to accomplish two tasks, the first is enabling HT from your motherboard's BIOS, the second one is to build a kernel that supports it.

If I'm not wrong you already build your kernel with the right options, now all you've got to do is to go on the motherboard's BIOS and enable HT, save and enjoy.

[kung.foo]

I have a question about HT.
I own a P4 3.2ghz, with HT currently enabled. Compiling the kernel for example right now, only uses up 50% of the Cpu power (as stated by system monitor). Which seems nice, "Hey, I still have half the power at my hands right now..."
Do the two CPU inside the one I own, run both with half speed, and then add up to the total speed, or are both running with 3.2ghz?? Also, is it really a wise choice to enable HT under Linux, as far as my experience goes, the scheduler is far good enough, that it wouldn't even be necessary...

[Nard`]

I have a question about HT.
I own a P4 3.2ghz, with HT currently enabled. Compiling the kernel for example right now, only uses up 50% of the Cpu power (as stated by system monitor). Which seems nice, "Hey, I still have half the power at my hands right now..."
Do the two CPU inside the one I own, run both with half speed, and then add up to the total speed, or are both running with 3.2ghz?? Also, is it really a wise choice to enable HT under Linux, as far as my experience goes, the scheduler is far good enough, that it wouldn't even be necessary...

I don't think you quite understand HT Hyperthreading works by having one physical processor split up into two logical ones, it does that by allowing for the fact that when the CPU is waiting to do something (i.e. waiting for hard disk read) it will let the other logical processor do something else. At least, that's what I think happens...

[kung.foo]

Yeah i kinda understand that it is only logical. So the "two" CPUs both run at full speed, say during compilation, because there is in fact only one of them...
Now this starts to sound like I'm a hardware moron