[LAU] How to turn off hyperthreading?

[david]

On 03/25/2013 01:15 PM, Len Ovens wrote:
>
> On Mon, March 25, 2013 1:39 pm, Jostein Chr. Andersen wrote:
>> On 03/25/2013 08:06 PM, david wrote:
>>> The laptop I'm considering (Zareason Verix 530) as replacement for my
>>> current one has a dual-core Intel i3 processor with hyperthreading.
>>> Zareason says there's no way to turn off HT in BIOS.
>>>
>>> I think folk on the list have said that HT causes problems with RT. So
>>> how can I disable hyperthreading?
>>
>> I can do like this in my Kubuntu system which have 8 kernels:
>>
>> sudo echo 0 > /sys/devices/system/node/node0/cpu0/online
>> sudo echo 0 > /sys/devices/system/node/node0/cpu2/online
>
> That should be all you need with two cores, turn off cpu 0 and 2, though
> most people turn off 1 and 3 :)
>> sudo echo 0 > /sys/devices/system/node/node0/cpu7/online
>
> Which is why the cpu 7 here.
>
> Linux sees the each core as two cpus, one for each thread. Not only might
> a thread be using too much time but there is also the overhead of context
> switching (invisible to the kernel) from one thread to the other. With
> hyper threading on, I can run jack at 64 frames with few xruns. With
> hyperthreading off, I can get down to 16 frames with guitarix running and
> no xruns. (10 year old single core p4 at 2.4G) Read up on some of the cnc
> projects where they require lower latency than audio. Lots of good info.

Thanks! Now I'm curious why a BIOS can't turn off HT ...

-- 
David
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http://clanjones.org/david/
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