topic Re: hyperthreading enabled/disabled? in Operating System - Linux

hyperthreading enabled/disabled?

Vijaya Kumar_3 — Thu, 06 Nov 2003 10:38:47 GMT

I have a Compaq DL380 G3 with 4 processors and 4 GB RAM. I am running redhat Linux 8.0

I need to know "Hyperthreading" is enabled in BIOS? How can i check that?

Thanks
Vijay

Re: hyperthreading enabled/disabled?

Vijaya Kumar_3 — Thu, 06 Nov 2003 10:39:27 GMT

Sorry...
I dont want to reboot.
I need a command line...

Thanks
Vijay

Re: hyperthreading enabled/disabled?

F Javier Gonzalez Marti — Thu, 06 Nov 2003 11:07:34 GMT

With top command?

This command shows the number of CPU in your machine.

Re: hyperthreading enabled/disabled?

Vijaya Kumar_3 — Thu, 06 Nov 2003 11:32:04 GMT

Thanks for ur quick reply...
what does that mean...
It shows 4 processors with CPU 0 to 4
What dows that mean?

Vijay

Re: hyperthreading enabled/disabled?

Umapathy S — Thu, 06 Nov 2003 12:00:30 GMT

Vijay,
For hyperthreading, you should be really running SMP Linux. Can you post the kernel version. I suppose RH 8.0 is not supporting hyperthreading. You may need to recompile the kernel with SMP support.

HTH,
Umapathy

Re: hyperthreading enabled/disabled?

Vijaya Kumar_3 — Thu, 06 Nov 2003 12:07:35 GMT

Thanks for ur reply Umapathy

Btw, I am running SMP Kernel
2.4.18-14smp

Thanks
Vijay

Re: hyperthreading enabled/disabled?

Umapathy S — Thu, 06 Nov 2003 12:18:02 GMT

Vijay,

What is there in /proc/cpu?

Since it a 4 physical processor machine, it should show 8 inside /proc/cpu. Otherwise, it is not supporting hyperthreading.

hth
Umapathy

Re: hyperthreading enabled/disabled?

Huc_1 — Thu, 06 Nov 2003 12:21:00 GMT

the following command should be able to tell you this!

# sysctl -A | grep -i "threa"

also have a look at

#procinfo

Hope this will help you

J-P

Re: hyperthreading enabled/disabled?

U.SivaKumar_2 — Fri, 07 Nov 2003 03:55:12 GMT

Hi,

You dont have hyper threading currently.
reboot the server.
Press F9 key to get in to BIOS

Go to Advanced options ( set the below value)

Processor Hyper-Threading enabled

Save BIOS config and reboot the server.

Now after linux has booted.

give

#top

which should show number of processors more than the actual (physical) number of processors.

regards,

U.SivaKumar

Re: hyperthreading enabled/disabled?

U.SivaKumar_2 — Fri, 07 Nov 2003 04:00:45 GMT

To be more precise , to confirm that hyper-threading is functioning in your setup . you should see 8 processors in top screen.

viz. 2 logical processor per 1 physical processor.

regards,

U.SivaKumar

Re: hyperthreading enabled/disabled?

K.C. Chan — Fri, 07 Nov 2003 09:16:51 GMT

Sorry, I believe you need to reboot for this. Basically you need to have this enable at the BIOS level. AFAIK, HT is available starting in 2.4.18 kernel.

Re: hyperthreading enabled/disabled?

Vijaya Kumar_3 — Fri, 07 Nov 2003 12:46:25 GMT

Thanks people.

Regards
Vijay

Re: hyperthreading enabled/disabled?

John Daily — Wed, 04 Feb 2004 10:51:16 GMT

FYI - A DL380 G3 can only have 2 Physical Processors - so if you see 4, Hyperthreading is turned on.

Re: hyperthreading enabled/disabled?

Olivier Drouin — Wed, 04 Feb 2004 10:55:32 GMT

You beat me @ it john.
HyperThreading is on by default, well, on hp/compaq machines...

Re: hyperthreading enabled/disabled?

Roberto Polli — Tue, 20 Apr 2004 04:15:40 GMT

Hi all:

cat /proc/cpu|grep ht

if this flag "ht" is present in /proc/cpu then hyperthreading is enabled.
Peace, R.

Re: hyperthreading enabled/disabled?

Martin P.J. Zinser — Tue, 20 Apr 2004 13:22:02 GMT

Hi,

this should be /proc/cpuinfo, not /proc/cpu (at least on my Fedora and SuSE systems).

Greetings, Martin

Re: hyperthreading enabled/disabled?

Hein van den Heuvel — Wed, 21 Apr 2004 00:03:40 GMT

Roberto wrote:

"if this flag "ht" is present in /proc/cpu then hyperthreading is enabled."

Hmm, I beg to differ. I believe that just means that the processor is ht capeable, not whether it is active or not.

Intuitively I'd say like U.SivaKumar just use top and see how many CPU's it lists. However, that could misguide you if the BOX is for example made for 4 CPUs, but only 2 are installed... with HT still showing 4 CPUs.

I think the best solution is:
grep -E "processor|physical id" /proc/cpuinfo
And even that is slightly inconsistent on my systems with:

My 4P dl560 running " SuSE SLES 8 (powered by UnitedLinux 1.0) (i586)\nKernel 2.4.21-138-smp (1)" With HT enabled shows:
grep -E "processor|physical id" /proc/cpuinfo
processor : 0
physical id : 0
processor : 1
physical id : 0
processor : 2
physical id : 1
processor : 3
physical id : 1
processor : 4
physical id : 2
processor : 5
physical id : 2
processor : 6
physical id : 3
processor : 7
physical id : 3

But on older box running "SuSE SLES 8 (powered by UnitedLinux 1.0) (i586)\nKernel 2.4.19-64GB-SMP (2)" and NO HT shows:
processor : 0
physical id : 0
processor : 1
physical id : 0
processor : 2
physical id : 0
processor : 3
physical id : 0

So yes you can see what is happening, but not clearly.

JP Huc wrote : "the following command should be able to tell you this!
# sysctl -A | grep -i "threa"

Hmmm... not on my box! (It just returns "kernel.threads-max = 14336")

And procinfo does tell me how many CPUs, but not whether they are virtual or physical.
So like the 'top' solution I could get a false negative when less then halve of the possible CPUs are physically installed.

vijay wrote: "what does that mean... It shows 4 processors with CPU 0 to 4"
It means you did not read carefully, or someoen is playing a joke on you.
4 CPUS would be labeled CPU0 thru CPU3 (or maybe my english is not sharp enough and your 'to' really meant 'up to, but not including :-).

John Daily had the keenest response and should get the 10 Points... if his timing had been better.

fwiw,
Hein.

Re: hyperthreading enabled/disabled?

Jeroen Peereboom — Wed, 21 Apr 2004 01:05:06 GMT

Hein,

nice analysis.

I just switched off hyperthreading on my DL360. I didn't check all responses here like you did, but the reply that a DL380 (and I hope a DL360 too) can have at most 2 CPU's triggered me. Using top I saw 4 CPUs. After rebooting and switching off hyperthreading top only showed 2.

JP.

Re: hyperthreading enabled/disabled?

Hein van den Heuvel — Wed, 21 Apr 2004 01:26:55 GMT

Jeroen,

Are you going to share with us why you are switching of Hyperthreading? If it is to evaluate the gain/losse s for it, please share that with us the findings with a rough description of the application!
(tight loops, large foot-print, little memory touched, lots of memory, oltp? web? a few, dozens or hundreds of processes per cpu? and so on.)

Met vriendelijke groetjes,
Hein.

Re: hyperthreading enabled/disabled?

Jeroen Peereboom — Wed, 21 Apr 2004 02:26:57 GMT

Hein,

don't be surprised but I'm not sure if I need to switch it off.

I'm installing a test Oracle RAC cluster. I was told that when using Oracle parallel queries you should not have hyperthreading enabled.

I have it on a question list for the Oracle consultant I will be talking to in the (near) future.

Groeten,

Jeroen P.