disable the hyper threading ON Linux

[Aaron]

Dan Stromberg wrote:
>
> Whether hyperthreading is faster or slower probably depends on your 
> workload.
>
> Granted, hyperthreading allows more of the CPU to be engaged at any 
> given moment, but it may also halve your Ln cache size.
>
> On Nov 28, 2007 11:06 AM, vadim <vadim at ovguide.com 
> <mailto:vadim at ovguide.com>> wrote:
>
>     Same here - BIOS is the only way to disable it. On a personal note, an
>     HT CPU performs faster than non HT CPU - tried that a few years back.
>     -V
>
>     David Chait wrote:
>     > I'm fairly certain that this is only done via the machine Bios,
>     not the OS.
>     >
>     > -David
>     >
>     >
>     > Santhosh kumar wrote:
>     >> Some one guide me how to disable the hyper threading on Dell
>     2650? I
>     >> am running rhel 3 update 6. Is there any way I can do this
>     >> modification from the OS level.
>     >>
>     >>
>     >>
>     >> Thanks in advance
>     >> Santhosh
>     >>
>     >>
>     >>
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That is correct.  Depending on what you are doing will determine the 
performance gain or loss.  Compression, decompression, 
encoding/transcoding, decryption, Oracle, MySQL all seem to benefit from 
HT when they have multiple threads or daemons.  I disable it on servers 
that have one or two heavy IO processes.  With other applications your 
milage may vary and you should perform your own benchmark testing.  I 
have found that one some weblogic/Jboss server deployments, I get more 
performance with it off.

If you are going to disable it, I would suggesting using the BIOS to 
control that.  Turning it off in the kernel just further cripples your 
performance, as the other logical processor is technically still on in 
the hardware, you just are not utilizing it.  That is almost akin to 
using UP kernel on SMP machines, sortof.


--Aaron