Any way to switch of hyperthreading in registry?

Hi,

I urgently need to switch off hyperthreading on my HP Pavilion DV6 core i7 720qm running Windows 7 Home Premium 64bit!

As I need to run a very processor intensive simulation software that only uses one thread and is taking minutes or hours for certain simulations, I am hoping to find a way to use at least a full core and not a half one.

I am not so lucky with my InsydeH2o BIOS F13 which has a only a handfull of adjustment options like system time and date but certainly no hyperthreading (HT)

I know you can turn off processors in the msconfig but that is not the same - windows still devides the remaining physical cores...

Booting into EFI shell would be another options as HT could be switched off there but I don t know how to add the shell to the bootmanager (how to configure easyBCD and/or GRUB?). Of course booting into EFI is not a visible option in my bios - even though the BIOS is, I understand, completely UEFI based and only emulates the old BIOS interface!

Maybe there is a registry key tweak or something else you guys know. I am sure there must be loads of programs/games out there that would benefit from a disabled HT!

Here is a link to my notebook drivers and specs: Select software and drivers HP Pavilion dv6-2090eo Entertainment Notebook PC - HP Customer Care (Australia - English)

I don't expect anyone can fix this (I spent already two weeks on this) but if you have an idea please let me know and post so others can see it too..

Thanks!:)

Exito

PS: I even looked into editing this BIOS which can be done with some effort and risk but even than it seems dozens of options but no hyperthreading.. only "core multi processing" which is likely just switching off cores but not HT. Info on InsdyeH2o BIOS editing are here: Insyde BIOS modding (dv4,dv5,dv6,dv7 at least)

Hi logicearth,

I really hope you are right. I am always open to change my mind as long as there is a good reason.

Task manager shows one out of 8 cores at 100% while the others do literally nothing. It is not so obvious though as the processing is passed on every second or so to the next core - so it appears as if all cores are on it - which they are but not at the same time. It becomes more obvious if you change the affinity of the application to a smaller number of cores.

Average CPU load of all 8 cores is never more than 13% with my application - pretty close to the theoretical 12.5% which is 1/8 of all cores (1/2 physical core) running at 100% the rest doing nothing.

I can see nothing that suggests that my application uses one full physical core which would be 1/4 or 25% overall as I have 4 physical cores. I do think my application could run up to twice as fast without the logical core. This should also be true for single threaded games after disabling HT by the way.. those who can disable it easily in the BIOS could just check this easily and post here perhaps...? Just make sure you have not much else running in the background.. :)

I really wish I am wrong and I can stop trying to switch off hyperthreading which seems impossible until a new BIOS might allow this.

I appreciate yours and everyones help and time,

exito

PS: I found somewhere in the windows development guidelines for hyperthreading (HT )that they recommend that system developers provide an option to switch off HT in the BIOS - perhaps until multithreaded apps are more common? Not sure but would make sense .. :)

exito100 said:

...I found somewhere in the windows development guidelines for hyperthreading (HT )that they recommend that system developers provide an option to switch off HT in the BIOS - perhaps until multithreaded apps are more common? Not sure but would make sense .. :)

Yep, the BIOS is the place to do that.

There is much debate as to whether hyperthreading is good or bad, depending on whether or not the program in question has been written to take advantage of it. The consensus at the moment seems to be that if you don't use programs designed to take advantage of it you may actually lose 2-3 percent of your overall CPU efficiency due to system overhead in trying to shunt processes off on what is in effect a "psuedo" core. (This info derived from gaming benchmarks in particular.)

I leave mine "on". I'm not a big-time gamer, so the potential loss of an insignificant 2-3 percent is acceptable to me when weighed against the boost I get when using programs designed to take advantage of it. :)

open Run > type in msconfig and click Ok> go on Boot tab > click Advanced options... > there you have to tick "Number of processors" and select from the dropdown list how many processors you want windows to "see" from those available.

Hopefully this will help someone :)

well, I did exactly what i described on my eeepc. It has an Atom N270, single core with HT and no way to disable it from bios. I found number of processors unticked so I just checked it and selected 1.
Now i think there might be a possibility that HT is still on and now windows uses not the entire cpu (without HT), but only 1 of 2 virtual cores .
So what do you think?

>You have the wrong idea of Hyperthreading. You are using a full core.

regedit will only use half the core,
iexplore will only use half the core when rendering a complicated page.

There are many other single threaded applications that can only get 50% of the core.

There are cases where hyperthreading has had, as you experienced, a negative impact on performance.

E.g., SQL Server support in a hyper-threaded environment
SQL Server support in a hyper-threaded environment

andBe aware: To Hyper or not to Hyper
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