[KLUG Members] Trying to understand why high number of Context Switches with the RHEL4.0 kernel versus the RHEL3.0.

[Chester Wisniewski]

Komal wrote:

>
>2) why are there so many Context switching (CS) happening, is it becasue 
>2.6 kernel is preemptive, or does the Red hat distribution has some 
>other advanced scheduling algorithms that is causing it. If so, is there 
>someway to increase the timeslice on the fly ?  
>
>3) changing kernel to 2.4 by using LD_ASSUME_KERNEL  - why does that not 
>help if it is case of just the 2.6 kernel behavior
>
>Both machines have similar configurations and has hyperthreading enabled 
>with 4 logical CPUs.
>RHEL3.0 kernel - is 2.4.21-15.ELsmp #1 SMP,   threading is NPTL 0.6
>RHEL4.0 kernel is   2.6.9-5.ELsmp #1 SMP,   getconf 
>GNU_LIBPTHREAD_VERSION is  NPTL 2.3.4
>
>  
>
I would attribute this to hyperthreading. Adam has insisted that 
hyperthreading is beneficial for him, which is great, however it has yet 
to prove anything useful to me. I would try disabling hyperthreading and 
seeing if the behavior gets closer to the 2.4 kernel.

>Regards,
>
>Komal
>
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>
Chet