Re: [LAU] How to turn off hyperthreading?

On Sun, 22 Dec 2013, Jeremy Jongepier wrote:
>> This option is the preferred way to isolate CPUs. The alternative,
>> manually setting the CPU mask of all tasks in the system, can cause
>> problems and suboptimal load balancer performance."
>
> Thanks for the valuable information! If you don't mind I'll add it to
> http://wiki.linuxaudio.org/wiki/system%20configuration

I don't mind, it is not my info after all :)
>
> I thought just disabling them like:
>
> CPU=( cpu1 cpu3 cpu5 cpu7 )
> for i in "${CPU[@]}"
> do
> echo 0 > /sys/devices/system/cpu/$i/online
> done
>
> would do the trick too but on my own system I still can't go lower than
> -p128 so hopefully the isolcpus parameter improves stability.

From the bit above, it would appear that "turning the cpu off" while the
system is running only stops the kernel from assigning new tasks to a cpu,
but does not move threads already assigned to a new cpu. Concidering that
you probably run that script pretty early at boot, probably everything
assigned to those cpus is system and will run till shutdown. (just a guess
on my part though) There are utilities that can push tasks from cpu to
cpu, but I am not familiar with them.

With hyperthreading on, i am still able to run my delta 66 at -p64 with no
xruns. With hyperthreading off I can run the same card at -p16 with
guitarix and no xruns. So hyperthreading only makes a difference (for me)
below -p64.

Of note, I moved the card to not only a clear irq PCI slot, but the pci
slot with the highest clear irq. I had a midi interface in the next higher
irq and had problems till I switched them around phyically.

This is an older computer... single core P4 at 2.4Ghz and 2.5G ram.

--
Len Ovens
www.ovenwerks.net
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