Turn off hyperthreading on dual core Atom?

Bruce Cran bruce at cran.org.uk
Mon Aug 29 19:55:12 UTC 2011

On 29/08/2011 18:24, Brett Glass wrote:
> With hyperthreading, the FreeBSD scheduler simply acts as if there are 
> 4 CPUs. Each "CPU" gets clock interrupts (which add overhead), and the 
> scheduler is naive about the fact that two of the "CPUs" are not 
> separate chips and could be held up if its mate has a heavy load. I do 
> not know if the supposed higher utilization of the resources on each 
> chip (including executing one thread while the CPU waits for data for 
> another) is worth it. What has your experience been?

Actually, the ULE scheduler does know about HyperThreading and the 
topology of such CPUs. I don't know what it does with the information, 
but it probably works to optimize cache usage etc.

Bruce Cran

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