CPU utilization

Maxim Sobolev sobomax at FreeBSD.org
Thu Apr 12 22:39:16 UTC 2007

Julian Elischer wrote:
> Robert Watson wrote:
>> On Thu, 12 Apr 2007, Dag-Erling Smørgrav wrote:
>>> Randall Stewart <rrs at cisco.com> writes:
>>>> machdep.hyperthreading_allowed: 0
>>> Note that enabling hyperthreading is more likely to harm performance 
>>> than to help it.  You should just disable it in the BIOS, and run a 
>>> UP kernel.
>> Historically this has been true, but some more recent results I've 
>> seen suggest that both hyperthreading hardware has improved, and the 
>> efficiency of our SMP implementation and scheduler has lead to it 
>> being more effective used. I would reevaluate this on more modern 
>> hardware and using a more recent kernel before assuming this remains 
>> true for your application.
> In addition to this, to answer the original question, I remember a 
> commit so that if you disable a cpu (or HT cpu) it doesn't get counted
> in the CPU % so if you have 2 cpus and disable one hten prior to that
> commit it was not possible to get > 50% busy but after that commit
> you could get 100% "of the available CPUs". That fix is not (I believe)
> in 6.2.

That's correct. The fix went in after RELENG_6_2 has been branched.


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