Initial 6.1 questions

Scott Long scottl at
Tue Jun 13 19:04:24 UTC 2006

Danial Thom wrote:
> --- Robert Watson <rwatson at> wrote:
>>On Tue, 13 Jun 2006, Danial Thom wrote:
>>>Maybe someone can explain this output. The
>>top line shows 99.6%idle. Is it 
>>>just showing CPU 0s stats on the top line?
>>Two types of measurements are taken: sampled
>>ticks regarding whether the 
>>system as a while is in {user, nice, system,
>>intr, idle}, and then sampling 
>>for individual processes.  Right now, the
>>system measurements are kept in a 
>>simple array of tick counters called cp_time. 
>>John Baldwin and others have 
>>changes that make these tick counters per-CPU. 
>>The lines at the top of 
>>top(1)'s output are derived from those tick
>>counters.  Ticks are measured on 
>>each CPU, so those are a summary across all
>>CPUs.  To add cpustat support, we 
>>need to merge John's patch to make cp_time
>>per-CPU (ie., different counters 
>>for different CPUs) and teach the userland
>>tools to retrieve them.  When you 
>>run top you'll notice that it adjusts the
>>measurements each refresh.  In 
>>effect, what it's doing is sampling the change
>>in tick counts over the window, 
>>pulling down the new values and calculating the
>>percentages of ticks in each 
>>"bucket" in the last window.
> That doesn't explain why the Top line shows 99.6%
> idle, but the cpu idle threads are showing
> significant usage. 
> I'm getting a constant 6000 Interrupts / Second
> on my em controller, yet top jumps all over the
> place; sitting at 99% idle for 10 seconds, then
> jumping to 50%, then somewhere in between. It
> seems completely unreliable. The load I'm
> applying is constant.
> DT

Be aware that there was a significant change made to if_em
in 7-CURRENT in Jan 2006 to improve load performance.  It'll
probably get backported for 6.2, but you might consider
looking at it before you make up your mind on 6.1 performance.


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