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Old 12-03-2003, 05:25 PM   #1
v8esprit
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simply put, how do I disable Hyperthreading?


I have a Sager 8890 laptop. Its a psycho notebook, a true desktop replacement. It uses an i856 SpringDale chipset. You should consider it the same as a desktop for all intents and purposes, though it does have a battery. I have a 2.6 Mhz processor running at 800Mhz FSB. Its also Hyperthreading compatible.

For reference:
(sorry no URLS)


I am currently running the Distributed.net client which is trying to crack the RC5-72 bit cipher. Its one of those background programs that runs low priority, but consumes all unused CPU cycles.

For reference:
(sorry no URLS)

Now I have conducted some of my own tests and I find that when running in hyperthreading mode, my performance drops off considerably relative to a single processor environment. Let me provide you with an example of the rc5-72 client log files:

One processor:
[Sep 16 06:21:33 UTC] RC5-72: Summary: 2 packets (2.00 stats units)
0.00:31:33.12 - [3,540,605 keys/s]

Two processor: (Hyperthreading)
[Nov 04 18:25:37 UTC] Automatic processor detection found 2 processors.
[Nov 04 18:38:37 UTC] RC5-72: Completed CA:6AB5BFD0:00000000 (1.00 stats units)
0.01:24:31.91 - [846,827 keys/s]
[Nov 04 18:38:37 UTC] RC5-72: Loaded CA:6AB5BFD2:00000000:1*2^32
[Nov 04 18:38:37 UTC] RC5-72: Summary: 3 packets (3.00 stats units)
0.02:23:27.42 - [1,277,942 keys/s]
[Nov 04 18:44:06 UTC] RC5-72: Completed CA:6AB5BFD1:00000000 (1.00 stats units)
0.01:25:03.30 - [841,618 keys/s]
[Nov 04 18:44:06 UTC] RC5-72: Loaded CA:6AB5BFD3:00000000:1*2^32
[Nov 04 18:44:06 UTC] RC5-72: Summary: 4 packets (4.00 stats units)
0.02:28:56.42 - [1,711,515 keys/s]

After each key is completed, the client provides a benchmark statistic. With 1 processesor, I get a 3.5 Mk/s and with the HT score, each virtual processor is doing about .8 Mk/s. When added together they average at about half if hyperthreading were disabled!

Has anyone done other benchmarks on highly computational processes and seen performance losses with and without hyperthreading? Currently, I think its ho-key crap and some of the benchmarks I have seen have only had ~10% improvement on multi-threaded processes. Well, clearly, this RC5-72 client is very multi-thread and it takes a serious performance hit.

So I have this laptop, and its on all the time. Its got Mandrake 9.2 on. In the lilo.conf file, the Enterprice kernel I run has the following parameters:

image=/boot/vmlinuz-enterprise
label="linux-enterpris"
root=/dev/hda2
initrd=/boot/initrd-enterprise.img
append="devfs=mount hdg=ide-scsi acpi=ht splash=silent"
read-only

What do I change to disable Hyperthreading?

Results you might have already thought of:
If I removed the acpi=ht value, no difference.
If I go into the BIOS and disable Hyperthreading, the laptop can't unpack the kernel.
If hyperthreading is disabled in BIOS, and I insert the install CD, it also can't unpack the kernel.
You look at the Mandrake Errata which covers HT problems:
(sorry no URLS)
It states to add 'nolapic' to your kernel flags, well that does squat.

Make this real easy for me. What should I put into the apostrophes:
append=" "

I place your answer into my kernel flags, go into BIOS, disable HT, and then boot that kernel. If that could work, I'd be overjoyed. I've been scratching my head on this one for a long time. I sure hope someone can help me out.

-Lox Thomson
 
Old 12-03-2003, 06:59 PM   #2
jeremy
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