Re: [LAU] How to turn off hyperthreading?

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To: linux audio users <linux-audio-user@...>
Date: Monday, March 25, 2013 - 11:15 pm

On Mon, March 25, 2013 1:39 pm, Jostein Chr. Andersen wrote:

That should be all you need with two cores, turn off cpu 0 and 2, though
most people turn off 1 and 3 :)

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.

Hyperthreading improves "performance" over all, but raises the latency
audio can run at without dropouts. Once you hit 4 cores though,
hyperthreading is more of a gimmick than a help.

Every second thread/cpu can also be disabled on the kernel command line in
grub:

isolcpus= cpu_number[, cpu_number,...]

The cnc people also use this to hide a cpu away from the OS so they can
have full access to that cpu for just their application without the OS
using it too.

--
Len Ovens
www.OvenWerks.net

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Messages in current thread:
Re: [LAU] How to turn off hyperthreading?, Len Ovens, (Mon Mar 25, 11:15 pm)
Re: [LAU] How to turn off hyperthreading?, david, (Tue Mar 26, 9:26 am)