[plug] Hyperthreading ... boot parameter to disable it?

[Dion]

>> A quick google seems to point to simply adding "noht" to your boot 
>> parameters.
>>     
>
> The Google should have shown you that the "noht" parameter is
> wishful thinking. :-) Sorry.
>   
Oops, not the first time I've looked life a fool, sorry about that. 
It does appear that noht was put forward with a patch for some 2.4.19 
ish kernels at the very least,
but has been abandoned.

>> Otherwise, does your bios not allow disabling of HT.
>>     
>
> Not when I'm connected remotely! :-)
>   
>
Now that does make it tricky. I did however find at

http://oracle-rac.blogspot.com/2005/12/disabling-cpus-on-linux-part-two.html

the following.

    Saturday, December 17, 2005
      Disabling CPUs on Linux- Part Two If the server is supporting
    Hyperthreading, Linux implements the following mechanism:

        * First all the physical CPU's are enabled and then
        * then the logical CPU's are enabled

    This means that all the possible combinations can be enabled by
    specifying the maxcpu parameter in the boot command mentioned in the
    earlier post. For instance if the server has more than one physical
    CPU it is not possible to test one physical CPU with Hyperthreading
    enabled.


As explained in the quote, you may be able to exploit this order of cpu 
enabling, by setting the boot parameter maxcpus=       
to the number of physical cpus you have. Thus disabling HT in an 
indirect manner.

Hope this is more useful.

D.

-- 
"Never ascribe to malice that which may adequately be explained by incompetence." - Napoleon Bonaparte