Re: hackbench: 2.6.12-rc6 vs. 2.6.12-rc6-RT-V0.7.48-06

[Ingo Molnar]

* Esben Nielsen <simlo@xxxxxxxxxx> wrote:

> Depends on the configuration options. If you used the same configs 
> they should be the same but if you activated PREEMPT_RT it should slow 
> things down due to the overhead of irq-threading and mutexes instead 
> of spinlocks - although I am surprised the factor is _that_ big!

one has to make sure the default debug options are disabled.  
(DEADLOCK_DETECT, PREEMPT_DEBUG, etc.) But even then there will be 
considerable overhead. Until recently, the overhead used to be even 
bigger. Note that hackbench is pretty much the worst-case for 
PREEMPT_RT: lots of locking and scheduling done and we compare the UP 
kernel to the SMP kernel in essence. (in fact PREEMPT_RT's locking is 
currently higher overhead than SMP)

	Ingo
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